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 $243.93   10.128%   $268.6352   $268.64   $268.65   $268.60  
  Purchase #2 $33.57   5.377%   $35.3751   $35.38   $35.40   $35.40  
  Purchase #3 $173.83   4.738%   $182.0661   $182.07   $182.05   $182.10  
  Purchase #4 $158.83   6.516%   $169.1794   $169.18   $169.20   $169.20  
  Purchase #5 $212.94   5.786%   $225.2607   $225.26   $225.25   $225.30  
  Purchase #6 $188.39   12.601%   $212.129   $212.13   $212.15   $212.10  
  Purchase #7 $201.53   6.793%   $215.2199   $215.22   $215.20   $215.20  
  7 purchase totals = $1,213.02       $1,307.8654   $1,307.88   $1,307.90   $1,307.90