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 $85.27   12.163%   $95.6414   $95.64   $95.65   $95.60  
  Purchase #2 $236.39   8.777%   $257.138   $257.14   $257.15   $257.10  
  Purchase #3 $55.53   13.421%   $62.9827   $62.98   $63.00   $63.00  
  Purchase #4 $74.38   6.461%   $79.1857   $79.19   $79.20   $79.20  
  Purchase #5 $210.40   13.712%   $239.25   $239.25   $239.25   $239.30  
  Purchase #6 $32.92   10.188%   $36.2739   $36.27   $36.25   $36.30  
  Purchase #7 $200.38   7.667%   $215.7431   $215.74   $215.75   $215.70  
  7 purchase totals = $895.27       $986.2148   $986.21   $986.25   $986.20