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 $93.26   3.739%   $96.747   $96.75   $96.75   $96.70  
  Purchase #2 $43.71   4.834%   $45.8229   $45.82   $45.80   $45.80  
  Purchase #3 $219.61   3.460%   $227.2085   $227.21   $227.20   $227.20  
  Purchase #4 $147.47   9.690%   $161.7598   $161.76   $161.75   $161.80  
  Purchase #5 $135.61   13.335%   $153.6936   $153.69   $153.70   $153.70  
  Purchase #6 $75.65   5.233%   $79.6088   $79.61   $79.60   $79.60  
  Purchase #7 $93.49   8.561%   $101.4937   $101.49   $101.50   $101.50  
  7 purchase totals = $808.80       $866.3343   $866.33   $866.30   $866.30