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 $87.34   6.178%   $92.7359   $92.74   $92.75   $92.70  
  Purchase #2 $73.42   8.767%   $79.8567   $79.86   $79.85   $79.90  
  Purchase #3 $75.64   9.287%   $82.6647   $82.66   $82.65   $82.70  
  Purchase #4 $197.33   4.592%   $206.3914   $206.39   $206.40   $206.40  
  Purchase #5 $90.25   13.852%   $102.7514   $102.75   $102.75   $102.80  
  Purchase #6 $237.40   5.404%   $250.2291   $250.23   $250.25   $250.20  
  Purchase #7 $168.63   12.739%   $190.1118   $190.11   $190.10   $190.10  
  7 purchase totals = $930.01       $1,004.7410   $1,004.74   $1,004.75   $1,004.80