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 $107.35   10.860%   $119.0082   $119.01   $119.00   $119.00  
  Purchase #2 $26.87   3.744%   $27.876   $27.88   $27.90   $27.90  
  Purchase #3 $170.97   4.326%   $178.3662   $178.37   $178.35   $178.40  
  Purchase #4 $178.54   9.311%   $195.1639   $195.16   $195.15   $195.20  
  Purchase #5 $108.34   11.488%   $120.7861   $120.79   $120.80   $120.80  
  Purchase #6 $67.33   10.141%   $74.1579   $74.16   $74.15   $74.20  
  Purchase #7 $42.53   10.207%   $46.871   $46.87   $46.85   $46.90  
  7 purchase totals = $701.93       $762.2293   $762.24   $762.20   $762.40