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 $51.77   8.193%   $56.0115   $56.01   $56.00   $56.00  
  Purchase #2 $194.36   5.837%   $205.7048   $205.70   $205.70   $205.70  
  Purchase #3 $50.56   5.586%   $53.3843   $53.38   $53.40   $53.40  
  Purchase #4 $121.38   7.816%   $130.8671   $130.87   $130.85   $130.90  
  Purchase #5 $212.66   5.650%   $224.6753   $224.68   $224.70   $224.70  
  Purchase #6 $190.83   11.497%   $212.7697   $212.77   $212.75   $212.80  
  Purchase #7 $45.31   11.820%   $50.6656   $50.67   $50.65   $50.70  
  7 purchase totals = $866.87       $934.0783   $934.08   $934.05   $934.20