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 $32.69   11.174%   $36.3428   $36.34   $36.35   $36.30  
  Purchase #2 $21.52   10.299%   $23.7363   $23.74   $23.75   $23.70  
  Purchase #3 $231.28   8.795%   $251.6211   $251.62   $251.60   $251.60  
  Purchase #4 $199.69   9.487%   $218.6346   $218.63   $218.65   $218.60  
  Purchase #5 $85.86   7.496%   $92.2961   $92.30   $92.30   $92.30  
  Purchase #6 $242.68   9.187%   $264.975   $264.98   $265.00   $265.00  
  Purchase #7 $164.35   13.494%   $186.5274   $186.53   $186.55   $186.50  
  7 purchase totals = $978.07       $1,074.1333   $1,074.14   $1,074.20   $1,074.00