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 $57.47   9.446%   $62.8986   $62.90   $62.90   $62.90  
  Purchase #2 $74.49   9.478%   $81.5502   $81.55   $81.55   $81.60  
  Purchase #3 $221.50   8.835%   $241.0695   $241.07   $241.05   $241.10  
  Purchase #4 $176.95   4.238%   $184.4491   $184.45   $184.45   $184.40  
  Purchase #5 $158.36   11.805%   $177.0544   $177.05   $177.05   $177.10  
  Purchase #6 $82.56   12.643%   $92.9981   $93.00   $93.00   $93.00  
  Purchase #7 $27.63   3.504%   $28.5982   $28.60   $28.60   $28.60  
  7 purchase totals = $798.96       $868.6181   $868.62   $868.60   $868.70