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 $76.94   5.651%   $81.2879   $81.29   $81.30   $81.30  
  Purchase #2 $176.67   8.809%   $192.2329   $192.23   $192.25   $192.20  
  Purchase #3 $165.40   3.746%   $171.5959   $171.60   $171.60   $171.60  
  Purchase #4 $67.66   7.399%   $72.6662   $72.67   $72.65   $72.70  
  Purchase #5 $165.35   4.346%   $172.5361   $172.54   $172.55   $172.50  
  Purchase #6 $237.62   10.562%   $262.7174   $262.72   $262.70   $262.70  
  Purchase #7 $13.89   9.338%   $15.187   $15.19   $15.20   $15.20  
  7 purchase totals = $903.53       $968.2234   $968.24   $968.25   $968.20