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 $67.69   13.713%   $76.9723   $76.97   $76.95   $77.00  
  Purchase #2 $54.71   11.203%   $60.8392   $60.84   $60.85   $60.80  
  Purchase #3 $37.29   9.802%   $40.9452   $40.95   $40.95   $40.90  
  Purchase #4 $139.46   8.436%   $151.2248   $151.22   $151.20   $151.20  
  Purchase #5 $245.57   13.662%   $279.1198   $279.12   $279.10   $279.10  
  Purchase #6 $221.67   10.198%   $244.2759   $244.28   $244.30   $244.30  
  Purchase #7 $153.87   4.681%   $161.0727   $161.07   $161.05   $161.10  
  7 purchase totals = $920.26       $1,014.4499   $1,014.45   $1,014.40   $1,014.40