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 $52.58   9.614%   $57.635   $57.64   $57.65   $57.60  
  Purchase #2 $189.69   8.587%   $205.9787   $205.98   $206.00   $206.00  
  Purchase #3 $126.67   13.143%   $143.3182   $143.32   $143.30   $143.30  
  Purchase #4 $45.46   6.429%   $48.3826   $48.38   $48.40   $48.40  
  Purchase #5 $106.43   6.608%   $113.4629   $113.46   $113.45   $113.50  
  Purchase #6 $231.34   6.611%   $246.6339   $246.63   $246.65   $246.60  
  Purchase #7 $33.41   8.362%   $36.2037   $36.20   $36.20   $36.20  
  7 purchase totals = $785.58       $851.6150   $851.61   $851.65   $851.60