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 $247.28   5.849%   $261.7434   $261.74   $261.75   $261.70  
  Purchase #2 $190.29   12.167%   $213.4426   $213.44   $213.45   $213.40  
  Purchase #3 $203.67   5.259%   $214.381   $214.38   $214.40   $214.40  
  Purchase #4 $65.67   12.773%   $74.058   $74.06   $74.05   $74.10  
  Purchase #5 $244.33   7.837%   $263.4781   $263.48   $263.50   $263.50  
  Purchase #6 $228.43   10.571%   $252.5773   $252.58   $252.60   $252.60  
  Purchase #7 $211.75   11.742%   $236.6137   $236.61   $236.60   $236.60  
  7 purchase totals = $1,391.42       $1,516.2941   $1,516.29   $1,516.35   $1,516.30