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 $242.51   10.499%   $267.9711   $267.97   $267.95   $268.00  
  Purchase #2 $185.99   11.739%   $207.8234   $207.82   $207.80   $207.80  
  Purchase #3 $18.76   11.136%   $20.8491   $20.85   $20.85   $20.80  
  Purchase #4 $210.43   9.403%   $230.2167   $230.22   $230.20   $230.20  
  Purchase #5 $200.59   6.186%   $212.9985   $213.00   $213.00   $213.00  
  Purchase #6 $223.69   12.738%   $252.1836   $252.18   $252.20   $252.20  
  Purchase #7 $97.25   5.650%   $102.7446   $102.74   $102.75   $102.70  
  7 purchase totals = $1,179.22       $1,294.7870   $1,294.78   $1,294.75   $1,294.70