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 $178.34   10.852%   $197.6935   $197.69   $197.70   $197.70  
  Purchase #2 $44.83   9.874%   $49.2565   $49.26   $49.25   $49.30  
  Purchase #3 $156.61   5.175%   $164.7146   $164.71   $164.70   $164.70  
  Purchase #4 $52.60   7.335%   $56.4582   $56.46   $56.45   $56.50  
  Purchase #5 $138.74   11.205%   $154.2858   $154.29   $154.30   $154.30  
  Purchase #6 $159.40   8.776%   $173.3889   $173.39   $173.40   $173.40  
  Purchase #7 $165.55   4.152%   $172.4236   $172.42   $172.40   $172.40  
  7 purchase totals = $896.07       $968.2211   $968.22   $968.20   $968.30