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 $179.72   8.638%   $195.2442   $195.24   $195.25   $195.20  
  Purchase #2 $62.27   11.331%   $69.3258   $69.33   $69.35   $69.30  
  Purchase #3 $160.97   11.584%   $179.6168   $179.62   $179.60   $179.60  
  Purchase #4 $202.73   10.768%   $224.56   $224.56   $224.55   $224.60  
  Purchase #5 $189.70   12.263%   $212.9629   $212.96   $212.95   $213.00  
  Purchase #6 $119.70   3.105%   $123.4167   $123.42   $123.40   $123.40  
  Purchase #7 $62.93   7.187%   $67.4528   $67.45   $67.45   $67.50  
  7 purchase totals = $978.02       $1,072.5792   $1,072.58   $1,072.55   $1,072.60