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 $63.86   7.344%   $68.5499   $68.55   $68.55   $68.50  
  Purchase #2 $127.79   5.191%   $134.4236   $134.42   $134.40   $134.40  
  Purchase #3 $242.44   5.846%   $256.613   $256.61   $256.60   $256.60  
  Purchase #4 $195.80   11.700%   $218.7086   $218.71   $218.70   $218.70  
  Purchase #5 $107.54   11.246%   $119.6339   $119.63   $119.65   $119.60  
  Purchase #6 $88.93   9.649%   $97.5109   $97.51   $97.50   $97.50  
  Purchase #7 $5.73   6.427%   $6.0983   $6.10   $6.10   $6.10  
  7 purchase totals = $832.09       $901.5382   $901.53   $901.50   $901.40