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 $224.88   3.567%   $232.9015   $232.90   $232.90   $232.90  
  Purchase #2 $15.48   7.678%   $16.6686   $16.67   $16.65   $16.70  
  Purchase #3 $24.38   4.862%   $25.5654   $25.57   $25.55   $25.60  
  Purchase #4 $190.91   5.828%   $202.0362   $202.04   $202.05   $202.00  
  Purchase #5 $151.34   6.121%   $160.6035   $160.60   $160.60   $160.60  
  Purchase #6 $99.42   5.841%   $105.2271   $105.23   $105.25   $105.20  
  Purchase #7 $150.99   3.136%   $155.725   $155.73   $155.75   $155.70  
  7 purchase totals = $857.40       $898.7273   $898.74   $898.75   $898.70