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 $53.36   12.360%   $59.9553   $59.96   $59.95   $60.00  
  Purchase #2 $40.79   12.650%   $45.9499   $45.95   $45.95   $45.90  
  Purchase #3 $238.82   7.246%   $256.1249   $256.12   $256.10   $256.10  
  Purchase #4 $186.41   9.586%   $204.2793   $204.28   $204.30   $204.30  
  Purchase #5 $130.65   5.485%   $137.8162   $137.82   $137.80   $137.80  
  Purchase #6 $119.51   13.166%   $135.2447   $135.24   $135.25   $135.20  
  Purchase #7 $249.58   12.715%   $281.3141   $281.31   $281.30   $281.30  
  7 purchase totals = $1,019.12       $1,120.6844   $1,120.68   $1,120.65   $1,120.60