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 $186.82   8.625%   $202.9332   $202.93   $202.95   $202.90  
  Purchase #2 $225.91   10.459%   $249.5379   $249.54   $249.55   $249.50  
  Purchase #3 $60.67   6.306%   $64.4959   $64.50   $64.50   $64.50  
  Purchase #4 $70.94   7.173%   $76.0285   $76.03   $76.05   $76.00  
  Purchase #5 $107.50   13.489%   $122.0007   $122.00   $122.00   $122.00  
  Purchase #6 $42.93   8.579%   $46.613   $46.61   $46.60   $46.60  
  Purchase #7 $86.33   4.872%   $90.536   $90.54   $90.55   $90.50  
  7 purchase totals = $781.10       $852.1452   $852.15   $852.20   $852.00