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 $246.94   7.441%   $265.3148   $265.31   $265.30   $265.30  
  Purchase #2 $85.99   7.593%   $92.5192   $92.52   $92.50   $92.50  
  Purchase #3 $134.31   11.278%   $149.4575   $149.46   $149.45   $149.50  
  Purchase #4 $5.95   9.202%   $6.4975   $6.50   $6.50   $6.50  
  Purchase #5 $227.25   11.568%   $253.5383   $253.54   $253.55   $253.50  
  Purchase #6 $246.56   4.543%   $257.7612   $257.76   $257.75   $257.80  
  Purchase #7 $248.47   11.251%   $276.4254   $276.43   $276.45   $276.40  
  7 purchase totals = $1,195.47       $1,301.5139   $1,301.52   $1,301.50   $1,301.50