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 $235.74   4.755%   $246.9494   $246.95   $246.95   $246.90  
  Purchase #2 $213.91   9.527%   $234.2892   $234.29   $234.30   $234.30  
  Purchase #3 $13.75   12.431%   $15.4593   $15.46   $15.45   $15.50  
  Purchase #4 $112.83   10.677%   $124.8769   $124.88   $124.90   $124.90  
  Purchase #5 $124.73   3.755%   $129.4136   $129.41   $129.40   $129.40  
  Purchase #6 $197.52   6.179%   $209.7248   $209.72   $209.70   $209.70  
  Purchase #7 $84.43   12.184%   $94.717   $94.72   $94.70   $94.70  
  7 purchase totals = $982.91       $1,055.4302   $1,055.43   $1,055.40   $1,055.40