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 $96.44   8.410%   $104.5506   $104.55   $104.55   $104.60  
  Purchase #2 $89.63   4.844%   $93.9717   $93.97   $93.95   $94.00  
  Purchase #3 $142.42   7.483%   $153.0773   $153.08   $153.10   $153.10  
  Purchase #4 $122.57   3.778%   $127.2007   $127.20   $127.20   $127.20  
  Purchase #5 $199.55   3.399%   $206.3327   $206.33   $206.35   $206.30  
  Purchase #6 $88.60   10.568%   $97.9632   $97.96   $97.95   $98.00  
  Purchase #7 $70.90   11.725%   $79.213   $79.21   $79.20   $79.20  
  7 purchase totals = $810.11       $862.3092   $862.30   $862.30   $862.40