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 $103.69   13.793%   $117.992   $117.99   $118.00   $118.00  
  Purchase #2 $217.83   7.858%   $234.9471   $234.95   $234.95   $234.90  
  Purchase #3 $223.52   7.650%   $240.6193   $240.62   $240.60   $240.60  
  Purchase #4 $117.74   5.332%   $124.0179   $124.02   $124.00   $124.00  
  Purchase #5 $237.71   12.874%   $268.3128   $268.31   $268.30   $268.30  
  Purchase #6 $244.29   12.612%   $275.0999   $275.10   $275.10   $275.10  
  Purchase #7 $30.93   13.770%   $35.1891   $35.19   $35.20   $35.20  
  7 purchase totals = $1,175.71       $1,296.1781   $1,296.18   $1,296.15   $1,296.10