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 $51.91   5.337%   $54.6804   $54.68   $54.70   $54.70  
  Purchase #2 $14.61   11.723%   $16.3227   $16.32   $16.30   $16.30  
  Purchase #3 $54.72   7.374%   $58.7551   $58.76   $58.75   $58.80  
  Purchase #4 $210.58   5.134%   $221.3912   $221.39   $221.40   $221.40  
  Purchase #5 $178.28   9.747%   $195.657   $195.66   $195.65   $195.70  
  Purchase #6 $224.67   4.674%   $235.1711   $235.17   $235.15   $235.20  
  Purchase #7 $17.52   11.465%   $19.5287   $19.53   $19.55   $19.50  
  7 purchase totals = $752.29       $801.5062   $801.51   $801.50   $801.60