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 $49.98   7.274%   $53.6155   $53.62   $53.60   $53.60  
  Purchase #2 $17.73   8.282%   $19.1984   $19.20   $19.20   $19.20  
  Purchase #3 $235.91   4.161%   $245.7262   $245.73   $245.75   $245.70  
  Purchase #4 $221.71   13.871%   $252.4634   $252.46   $252.45   $252.50  
  Purchase #5 $70.91   8.374%   $76.848   $76.85   $76.85   $76.80  
  Purchase #6 $7.61   5.797%   $8.0512   $8.05   $8.05   $8.10  
  Purchase #7 $97.82   13.414%   $110.9416   $110.94   $110.95   $110.90  
  7 purchase totals = $701.67       $766.8443   $766.85   $766.85   $766.80