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 $206.75   6.554%   $220.3004   $220.30   $220.30   $220.30  
  Purchase #2 $245.55   13.390%   $278.4291   $278.43   $278.45   $278.40  
  Purchase #3 $126.77   13.845%   $144.3213   $144.32   $144.30   $144.30  
  Purchase #4 $49.52   3.251%   $51.1299   $51.13   $51.15   $51.10  
  Purchase #5 $18.83   4.817%   $19.737   $19.74   $19.75   $19.70  
  Purchase #6 $231.26   8.299%   $250.4523   $250.45   $250.45   $250.50  
  Purchase #7 $118.89   11.794%   $132.9119   $132.91   $132.90   $132.90  
  7 purchase totals = $997.57       $1,097.2819   $1,097.28   $1,097.30   $1,097.20