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 $116.63   12.767%   $131.5202   $131.52   $131.50   $131.50  
  Purchase #2 $126.72   13.299%   $143.5725   $143.57   $143.55   $143.60  
  Purchase #3 $68.93   7.454%   $74.068   $74.07   $74.05   $74.10  
  Purchase #4 $92.25   6.126%   $97.9012   $97.90   $97.90   $97.90  
  Purchase #5 $167.47   10.725%   $185.4312   $185.43   $185.45   $185.40  
  Purchase #6 $72.41   6.497%   $77.1145   $77.11   $77.10   $77.10  
  Purchase #7 $8.74   3.214%   $9.0209   $9.02   $9.00   $9.00  
  7 purchase totals = $653.15       $718.6285   $718.62   $718.55   $718.60