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 $71.37   6.479%   $75.9941   $75.99   $76.00   $76.00  
  Purchase #2 $131.62   3.290%   $135.9503   $135.95   $135.95   $136.00  
  Purchase #3 $130.96   13.601%   $148.7719   $148.77   $148.75   $148.80  
  Purchase #4 $170.87   3.862%   $177.469   $177.47   $177.45   $177.50  
  Purchase #5 $244.48   3.870%   $253.9414   $253.94   $253.95   $253.90  
  Purchase #6 $206.46   6.276%   $219.4174   $219.42   $219.40   $219.40  
  Purchase #7 $229.64   4.428%   $239.8085   $239.81   $239.80   $239.80  
  7 purchase totals = $1,185.40       $1,251.3526   $1,251.35   $1,251.30   $1,251.40