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 $181.81   11.579%   $202.8618   $202.86   $202.85   $202.90  
  Purchase #2 $85.94   13.639%   $97.6614   $97.66   $97.65   $97.70  
  Purchase #3 $52.71   7.384%   $56.6021   $56.60   $56.60   $56.60  
  Purchase #4 $62.98   13.341%   $71.3822   $71.38   $71.40   $71.40  
  Purchase #5 $216.55   13.660%   $246.1307   $246.13   $246.15   $246.10  
  Purchase #6 $51.64   9.782%   $56.6914   $56.69   $56.70   $56.70  
  Purchase #7 $59.56   12.195%   $66.8233   $66.82   $66.80   $66.80  
  7 purchase totals = $711.19       $798.1529   $798.14   $798.15   $798.20