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 $70.96   3.366%   $73.3485   $73.35   $73.35   $73.30  
  Purchase #2 $179.91   8.421%   $195.0602   $195.06   $195.05   $195.10  
  Purchase #3 $119.69   5.568%   $126.3543   $126.35   $126.35   $126.40  
  Purchase #4 $150.57   13.618%   $171.0746   $171.07   $171.05   $171.10  
  Purchase #5 $82.97   6.567%   $88.4186   $88.42   $88.40   $88.40  
  Purchase #6 $8.86   13.686%   $10.0726   $10.07   $10.05   $10.10  
  Purchase #7 $202.39   7.316%   $217.1969   $217.20   $217.20   $217.20  
  7 purchase totals = $815.35       $881.5257   $881.52   $881.45   $881.60