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 $130.25   12.396%   $146.3958   $146.40   $146.40   $146.40  
  Purchase #2 $48.59   10.642%   $53.7609   $53.76   $53.75   $53.80  
  Purchase #3 $79.28   4.252%   $82.651   $82.65   $82.65   $82.70  
  Purchase #4 $116.34   5.727%   $123.0028   $123.00   $123.00   $123.00  
  Purchase #5 $228.39   3.226%   $235.7579   $235.76   $235.75   $235.80  
  Purchase #6 $106.47   12.271%   $119.5349   $119.53   $119.55   $119.50  
  Purchase #7 $84.33   11.200%   $93.775   $93.78   $93.80   $93.80  
  7 purchase totals = $793.65       $854.8783   $854.88   $854.90   $855.00