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 $54.62   8.700%   $59.3719   $59.37   $59.35   $59.40  
  Purchase #2 $214.68   9.515%   $235.1068   $235.11   $235.10   $235.10  
  Purchase #3 $55.28   12.257%   $62.0557   $62.06   $62.05   $62.10  
  Purchase #4 $89.81   8.598%   $97.5319   $97.53   $97.55   $97.50  
  Purchase #5 $56.98   4.166%   $59.3538   $59.35   $59.35   $59.40  
  Purchase #6 $116.66   3.871%   $121.1759   $121.18   $121.20   $121.20  
  Purchase #7 $208.80   11.364%   $232.528   $232.53   $232.55   $232.50  
  7 purchase totals = $796.83       $867.1240   $867.13   $867.15   $867.20