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 $67.35   9.535%   $73.7718   $73.77   $73.75   $73.80  
  Purchase #2 $27.73   8.586%   $30.1109   $30.11   $30.10   $30.10  
  Purchase #3 $127.66   3.164%   $131.6992   $131.70   $131.70   $131.70  
  Purchase #4 $79.86   9.269%   $87.2622   $87.26   $87.25   $87.30  
  Purchase #5 $75.80   12.634%   $85.3766   $85.38   $85.40   $85.40  
  Purchase #6 $111.27   3.444%   $115.1021   $115.10   $115.10   $115.10  
  Purchase #7 $138.29   9.860%   $151.9254   $151.93   $151.95   $151.90  
  7 purchase totals = $627.96       $675.2482   $675.25   $675.25   $675.30