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 $202.53   11.732%   $226.2908   $226.29   $226.30   $226.30  
  Purchase #2 $144.92   6.449%   $154.2659   $154.27   $154.25   $154.30  
  Purchase #3 $111.32   8.229%   $120.4805   $120.48   $120.50   $120.50  
  Purchase #4 $9.64   10.443%   $10.6467   $10.65   $10.65   $10.60  
  Purchase #5 $31.87   5.177%   $33.5199   $33.52   $33.50   $33.50  
  Purchase #6 $133.53   9.508%   $146.226   $146.23   $146.25   $146.20  
  Purchase #7 $247.77   5.559%   $261.5435   $261.54   $261.55   $261.50  
  7 purchase totals = $881.58       $952.9733   $952.98   $953.00   $952.90