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 $132.41   3.164%   $136.5995   $136.60   $136.60   $136.60  
  Purchase #2 $113.86   8.599%   $123.6508   $123.65   $123.65   $123.70  
  Purchase #3 $51.34   5.296%   $54.059   $54.06   $54.05   $54.10  
  Purchase #4 $243.79   4.446%   $254.6289   $254.63   $254.65   $254.60  
  Purchase #5 $161.74   13.321%   $183.2854   $183.29   $183.30   $183.30  
  Purchase #6 $183.37   13.459%   $208.0498   $208.05   $208.05   $208.00  
  Purchase #7 $48.27   3.455%   $49.9377   $49.94   $49.95   $49.90  
  7 purchase totals = $934.78       $1,010.2111   $1,010.22   $1,010.25   $1,010.20