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 $121.56   5.301%   $128.0039   $128.00   $128.00   $128.00  
  Purchase #2 $71.86   5.650%   $75.9201   $75.92   $75.90   $75.90  
  Purchase #3 $52.74   5.765%   $55.7805   $55.78   $55.80   $55.80  
  Purchase #4 $132.53   12.285%   $148.8113   $148.81   $148.80   $148.80  
  Purchase #5 $68.97   9.534%   $75.5456   $75.55   $75.55   $75.50  
  Purchase #6 $11.33   12.271%   $12.7203   $12.72   $12.70   $12.70  
  Purchase #7 $224.76   11.622%   $250.8816   $250.88   $250.90   $250.90  
  7 purchase totals = $683.75       $747.6633   $747.66   $747.65   $747.60