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 $183.66   6.622%   $195.822   $195.82   $195.80   $195.80  
  Purchase #2 $234.31   13.495%   $265.9301   $265.93   $265.95   $265.90  
  Purchase #3 $175.49   7.422%   $188.5149   $188.51   $188.50   $188.50  
  Purchase #4 $108.58   13.415%   $123.146   $123.15   $123.15   $123.10  
  Purchase #5 $16.79   10.344%   $18.5268   $18.53   $18.55   $18.50  
  Purchase #6 $10.51   3.389%   $10.8662   $10.87   $10.85   $10.90  
  Purchase #7 $62.78   9.694%   $68.8659   $68.87   $68.85   $68.90  
  7 purchase totals = $792.12       $871.6719   $871.68   $871.65   $871.60