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 $113.47   11.711%   $126.7585   $126.76   $126.75   $126.80  
  Purchase #2 $126.86   6.439%   $135.0285   $135.03   $135.05   $135.00  
  Purchase #3 $93.79   13.292%   $106.2566   $106.26   $106.25   $106.30  
  Purchase #4 $69.54   12.578%   $78.2867   $78.29   $78.30   $78.30  
  Purchase #5 $178.96   7.835%   $192.9815   $192.98   $193.00   $193.00  
  Purchase #6 $61.44   5.669%   $64.923   $64.92   $64.90   $64.90  
  Purchase #7 $79.71   5.258%   $83.9012   $83.90   $83.90   $83.90  
  7 purchase totals = $723.77       $788.1360   $788.14   $788.15   $788.20