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 $241.93   8.526%   $262.557   $262.56   $262.55   $262.60  
  Purchase #2 $77.70   3.677%   $80.557   $80.56   $80.55   $80.60  
  Purchase #3 $101.98   8.423%   $110.5698   $110.57   $110.55   $110.60  
  Purchase #4 $116.65   4.511%   $121.9121   $121.91   $121.90   $121.90  
  Purchase #5 $134.25   7.340%   $144.104   $144.10   $144.10   $144.10  
  Purchase #6 $242.86   3.370%   $251.0444   $251.04   $251.05   $251.00  
  Purchase #7 $77.45   9.103%   $84.5003   $84.50   $84.50   $84.50  
  7 purchase totals = $992.82       $1,055.2446   $1,055.24   $1,055.20   $1,055.30