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 $15.65   13.270%   $17.7268   $17.73   $17.75   $17.70  
  Purchase #2 $163.32   8.757%   $177.6219   $177.62   $177.60   $177.60  
  Purchase #3 $186.98   10.146%   $205.951   $205.95   $205.95   $206.00  
  Purchase #4 $141.86   12.316%   $159.3315   $159.33   $159.35   $159.30  
  Purchase #5 $243.83   7.437%   $261.9636   $261.96   $261.95   $262.00  
  Purchase #6 $36.38   6.797%   $38.8527   $38.85   $38.85   $38.90  
  Purchase #7 $167.82   9.165%   $183.2007   $183.20   $183.20   $183.20  
  7 purchase totals = $955.84       $1,044.6482   $1,044.64   $1,044.65   $1,044.70