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 $102.64   10.393%   $113.3074   $113.31   $113.30   $113.30  
  Purchase #2 $126.69   6.525%   $134.9565   $134.96   $134.95   $135.00  
  Purchase #3 $167.50   6.781%   $178.8582   $178.86   $178.85   $178.90  
  Purchase #4 $132.40   6.676%   $141.239   $141.24   $141.25   $141.20  
  Purchase #5 $81.39   5.211%   $85.6312   $85.63   $85.65   $85.60  
  Purchase #6 $21.27   9.773%   $23.3487   $23.35   $23.35   $23.30  
  Purchase #7 $43.79   6.581%   $46.6718   $46.67   $46.65   $46.70  
  7 purchase totals = $675.68       $724.0128   $724.02   $724.00   $724.00