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 $248.74   8.220%   $269.1864   $269.19   $269.20   $269.20  
  Purchase #2 $224.35   13.161%   $253.8767   $253.88   $253.90   $253.90  
  Purchase #3 $22.39   11.866%   $25.0468   $25.05   $25.05   $25.00  
  Purchase #4 $51.39   13.356%   $58.2536   $58.25   $58.25   $58.30  
  Purchase #5 $93.69   6.355%   $99.644   $99.64   $99.65   $99.60  
  Purchase #6 $161.26   9.409%   $176.433   $176.43   $176.45   $176.40  
  Purchase #7 $28.69   3.212%   $29.6115   $29.61   $29.60   $29.60  
  7 purchase totals = $830.51       $912.0520   $912.05   $912.10   $912.00