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 $46.71   13.539%   $53.0341   $53.03   $53.05   $53.00  
  Purchase #2 $156.50   9.165%   $170.8432   $170.84   $170.85   $170.80  
  Purchase #3 $25.30   3.583%   $26.2065   $26.21   $26.20   $26.20  
  Purchase #4 $65.85   8.823%   $71.6599   $71.66   $71.65   $71.70  
  Purchase #5 $17.53   13.805%   $19.95   $19.95   $19.95   $20.00  
  Purchase #6 $85.72   6.290%   $91.1118   $91.11   $91.10   $91.10  
  Purchase #7 $243.73   8.274%   $263.8962   $263.90   $263.90   $263.90  
  7 purchase totals = $641.34       $696.7017   $696.70   $696.70   $696.70