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 $81.50   13.778%   $92.7291   $92.73   $92.75   $92.70  
  Purchase #2 $50.73   3.776%   $52.6456   $52.65   $52.65   $52.60  
  Purchase #3 $67.32   8.300%   $72.9076   $72.91   $72.90   $72.90  
  Purchase #4 $213.34   13.811%   $242.8044   $242.80   $242.80   $242.80  
  Purchase #5 $25.93   10.343%   $28.6119   $28.61   $28.60   $28.60  
  Purchase #6 $126.33   5.258%   $132.9724   $132.97   $132.95   $133.00  
  Purchase #7 $119.35   13.863%   $135.8955   $135.90   $135.90   $135.90  
  7 purchase totals = $684.50       $758.5665   $758.57   $758.55   $758.50