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 $62.37   10.416%   $68.8665   $68.87   $68.85   $68.90  
  Purchase #2 $55.92   9.393%   $61.1726   $61.17   $61.15   $61.20  
  Purchase #3 $92.80   9.304%   $101.4341   $101.43   $101.45   $101.40  
  Purchase #4 $77.68   13.830%   $88.4231   $88.42   $88.40   $88.40  
  Purchase #5 $142.81   7.566%   $153.615   $153.62   $153.60   $153.60  
  Purchase #6 $161.75   8.337%   $175.2351   $175.24   $175.25   $175.20  
  Purchase #7 $82.26   8.537%   $89.2825   $89.28   $89.30   $89.30  
  7 purchase totals = $675.59       $738.0289   $738.03   $738.00   $738.00