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 $201.32   11.269%   $224.0068   $224.01   $224.00   $224.00  
  Purchase #2 $91.52   11.528%   $102.0704   $102.07   $102.05   $102.10  
  Purchase #3 $164.79   10.310%   $181.7798   $181.78   $181.80   $181.80  
  Purchase #4 $152.66   13.449%   $173.1912   $173.19   $173.20   $173.20  
  Purchase #5 $129.86   10.224%   $143.1369   $143.14   $143.15   $143.10  
  Purchase #6 $113.98   9.711%   $125.0486   $125.05   $125.05   $125.00  
  Purchase #7 $239.61   9.134%   $261.496   $261.50   $261.50   $261.50  
  7 purchase totals = $1,093.74       $1,210.7297   $1,210.74   $1,210.75   $1,210.70