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 $46.38   12.635%   $52.2401   $52.24   $52.25   $52.20  
  Purchase #2 $224.97   5.581%   $237.5256   $237.53   $237.55   $237.50  
  Purchase #3 $146.89   5.414%   $154.8426   $154.84   $154.85   $154.80  
  Purchase #4 $204.91   8.685%   $222.7064   $222.71   $222.70   $222.70  
  Purchase #5 $210.61   6.398%   $224.0848   $224.08   $224.10   $224.10  
  Purchase #6 $242.90   5.669%   $256.67   $256.67   $256.65   $256.70  
  Purchase #7 $115.55   10.290%   $127.4401   $127.44   $127.45   $127.40  
  7 purchase totals = $1,192.21       $1,275.5096   $1,275.51   $1,275.55   $1,275.40