Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $151.37   13.765%   $172.2061   $172.21   $172.20   $172.20  
  Purchase #2 $236.92   12.786%   $267.2126   $267.21   $267.20   $267.20  
  Purchase #3 $210.48   11.208%   $234.0706   $234.07   $234.05   $234.10  
  Purchase #4 $172.43   9.467%   $188.7539   $188.75   $188.75   $188.80  
  Purchase #5 $222.38   5.555%   $234.7332   $234.73   $234.75   $234.70  
  Purchase #6 $163.47   13.683%   $185.8376   $185.84   $185.85   $185.80  
  Purchase #7 $246.99   12.331%   $277.4463   $277.45   $277.45   $277.40  
  7 purchase totals = $1,404.04       $1,560.2603   $1,560.26   $1,560.25   $1,560.20