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 $165.79   7.307%   $177.9043   $177.90   $177.90   $177.90  
  Purchase #2 $216.94   8.710%   $235.8355   $235.84   $235.85   $235.80  
  Purchase #3 $208.97   7.452%   $224.5424   $224.54   $224.55   $224.50  
  Purchase #4 $75.66   3.863%   $78.5827   $78.58   $78.60   $78.60  
  Purchase #5 $149.94   5.614%   $158.3576   $158.36   $158.35   $158.40  
  Purchase #6 $227.82   11.226%   $253.3951   $253.40   $253.40   $253.40  
  Purchase #7 $209.38   4.103%   $217.9709   $217.97   $217.95   $218.00  
  7 purchase totals = $1,254.50       $1,346.5885   $1,346.59   $1,346.60   $1,346.60