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 $131.68   7.665%   $141.7733   $141.77   $141.75   $141.80  
  Purchase #2 $236.32   3.824%   $245.3569   $245.36   $245.35   $245.40  
  Purchase #3 $60.99   3.174%   $62.9258   $62.93   $62.95   $62.90  
  Purchase #4 $154.60   5.651%   $163.3364   $163.34   $163.35   $163.30  
  Purchase #5 $93.80   3.587%   $97.1646   $97.16   $97.15   $97.20  
  Purchase #6 $50.79   7.537%   $54.618   $54.62   $54.60   $54.60  
  Purchase #7 $68.91   3.107%   $71.051   $71.05   $71.05   $71.10  
  7 purchase totals = $797.09       $836.2260   $836.23   $836.20   $836.30