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 $237.29   5.203%   $249.6362   $249.64   $249.65   $249.60  
  Purchase #2 $46.66   6.494%   $49.6901   $49.69   $49.70   $49.70  
  Purchase #3 $167.36   13.654%   $190.2113   $190.21   $190.20   $190.20  
  Purchase #4 $33.76   11.565%   $37.6643   $37.66   $37.65   $37.70  
  Purchase #5 $157.84   6.645%   $168.3285   $168.33   $168.35   $168.30  
  Purchase #6 $220.42   11.697%   $246.2025   $246.20   $246.20   $246.20  
  Purchase #7 $19.61   12.185%   $21.9995   $22.00   $22.00   $22.00  
  7 purchase totals = $882.94       $963.7324   $963.73   $963.75   $963.70