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 $108.97   8.828%   $118.5899   $118.59   $118.60   $118.60  
  Purchase #2 $175.75   9.220%   $191.9542   $191.95   $191.95   $192.00  
  Purchase #3 $12.82   13.327%   $14.5285   $14.53   $14.55   $14.50  
  Purchase #4 $100.84   11.702%   $112.6403   $112.64   $112.65   $112.60  
  Purchase #5 $201.82   4.218%   $210.3328   $210.33   $210.35   $210.30  
  Purchase #6 $131.38   4.305%   $137.0359   $137.04   $137.05   $137.00  
  Purchase #7 $63.45   9.833%   $69.689   $69.69   $69.70   $69.70  
  7 purchase totals = $795.03       $854.7706   $854.77   $854.85   $854.70