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 $20.67   7.265%   $22.1717   $22.17   $22.15   $22.20  
  Purchase #2 $30.88   10.502%   $34.123   $34.12   $34.10   $34.10  
  Purchase #3 $31.92   13.418%   $36.203   $36.20   $36.20   $36.20  
  Purchase #4 $117.59   5.811%   $124.4232   $124.42   $124.40   $124.40  
  Purchase #5 $45.45   12.695%   $51.2199   $51.22   $51.20   $51.20  
  Purchase #6 $81.34   3.627%   $84.2902   $84.29   $84.30   $84.30  
  Purchase #7 $130.60   11.873%   $146.1061   $146.11   $146.10   $146.10  
  7 purchase totals = $458.45       $498.5371   $498.53   $498.45   $498.50