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 $249.97   10.219%   $275.5144   $275.51   $275.50   $275.50  
  Purchase #2 $207.29   13.666%   $235.6183   $235.62   $235.60   $235.60  
  Purchase #3 $43.75   6.345%   $46.5259   $46.53   $46.55   $46.50  
  Purchase #4 $247.47   5.357%   $260.727   $260.73   $260.75   $260.70  
  Purchase #5 $133.90   7.289%   $143.66   $143.66   $143.65   $143.70  
  Purchase #6 $69.99   3.497%   $72.4376   $72.44   $72.45   $72.40  
  Purchase #7 $199.95   6.433%   $212.8128   $212.81   $212.80   $212.80  
  7 purchase totals = $1,152.32       $1,247.2960   $1,247.30   $1,247.30   $1,247.20