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 $52.82   11.680%   $58.9894   $58.99   $59.00   $59.00  
  Purchase #2 $169.68   5.645%   $179.2584   $179.26   $179.25   $179.30  
  Purchase #3 $139.96   4.592%   $146.387   $146.39   $146.40   $146.40  
  Purchase #4 $170.54   6.703%   $181.9713   $181.97   $181.95   $182.00  
  Purchase #5 $154.43   4.843%   $161.909   $161.91   $161.90   $161.90  
  Purchase #6 $188.35   10.858%   $208.801   $208.80   $208.80   $208.80  
  Purchase #7 $237.93   8.802%   $258.8726   $258.87   $258.85   $258.90  
  7 purchase totals = $1,113.71       $1,196.1887   $1,196.19   $1,196.15   $1,196.30