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 $98.76   4.159%   $102.8674   $102.87   $102.85   $102.90  
  Purchase #2 $221.35   4.281%   $230.826   $230.83   $230.85   $230.80  
  Purchase #3 $36.77   6.404%   $39.1248   $39.12   $39.10   $39.10  
  Purchase #4 $47.27   5.762%   $49.9937   $49.99   $50.00   $50.00  
  Purchase #5 $249.34   4.301%   $260.0641   $260.06   $260.05   $260.10  
  Purchase #6 $95.69   12.510%   $107.6608   $107.66   $107.65   $107.70  
  Purchase #7 $156.66   10.439%   $173.0137   $173.01   $173.00   $173.00  
  7 purchase totals = $905.84       $963.5505   $963.54   $963.50   $963.60