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 $98.67   5.865%   $104.457   $104.46   $104.45   $104.50  
  Purchase #2 $142.37   12.851%   $160.666   $160.67   $160.65   $160.70  
  Purchase #3 $143.71   7.325%   $154.2368   $154.24   $154.25   $154.20  
  Purchase #4 $121.45   3.247%   $125.3935   $125.39   $125.40   $125.40  
  Purchase #5 $113.86   13.214%   $128.9055   $128.91   $128.90   $128.90  
  Purchase #6 $31.26   3.593%   $32.3832   $32.38   $32.40   $32.40  
  Purchase #7 $232.83   3.470%   $240.9092   $240.91   $240.90   $240.90  
  7 purchase totals = $884.15       $946.9512   $946.96   $946.95   $947.00