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 $248.30   6.216%   $263.7343   $263.73   $263.75   $263.70  
  Purchase #2 $132.77   3.418%   $137.3081   $137.31   $137.30   $137.30  
  Purchase #3 $13.68   9.714%   $15.0089   $15.01   $15.00   $15.00  
  Purchase #4 $54.50   12.276%   $61.1904   $61.19   $61.20   $61.20  
  Purchase #5 $67.29   11.713%   $75.1717   $75.17   $75.15   $75.20  
  Purchase #6 $141.45   4.593%   $147.9468   $147.95   $147.95   $147.90  
  Purchase #7 $244.60   9.539%   $267.9324   $267.93   $267.95   $267.90  
  7 purchase totals = $902.59       $968.2926   $968.29   $968.30   $968.20