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 $73.96   3.781%   $76.7564   $76.76   $76.75   $76.80  
  Purchase #2 $25.83   11.618%   $28.8309   $28.83   $28.85   $28.80  
  Purchase #3 $181.42   12.727%   $204.5093   $204.51   $204.50   $204.50  
  Purchase #4 $21.34   10.262%   $23.5299   $23.53   $23.55   $23.50  
  Purchase #5 $60.58   5.552%   $63.9434   $63.94   $63.95   $63.90  
  Purchase #6 $46.70   6.241%   $49.6145   $49.61   $49.60   $49.60  
  Purchase #7 $245.42   9.163%   $267.9078   $267.91   $267.90   $267.90  
  7 purchase totals = $655.25       $715.0922   $715.09   $715.10   $715.00