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 $41.51   12.210%   $46.5784   $46.58   $46.60   $46.60  
  Purchase #2 $59.92   5.611%   $63.2821   $63.28   $63.30   $63.30  
  Purchase #3 $212.33   7.434%   $228.1146   $228.11   $228.10   $228.10  
  Purchase #4 $85.95   6.480%   $91.5196   $91.52   $91.50   $91.50  
  Purchase #5 $182.49   8.758%   $198.4725   $198.47   $198.45   $198.50  
  Purchase #6 $151.85   5.677%   $160.4705   $160.47   $160.45   $160.50  
  Purchase #7 $164.66   7.478%   $176.9733   $176.97   $176.95   $177.00  
  7 purchase totals = $898.71       $965.4110   $965.40   $965.35   $965.50