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 $66.74   7.245%   $71.5753   $71.58   $71.60   $71.60  
  Purchase #2 $86.43   10.358%   $95.3824   $95.38   $95.40   $95.40  
  Purchase #3 $72.39   4.206%   $75.4347   $75.43   $75.45   $75.40  
  Purchase #4 $226.88   6.224%   $241.001   $241.00   $241.00   $241.00  
  Purchase #5 $225.25   5.803%   $238.3213   $238.32   $238.30   $238.30  
  Purchase #6 $48.77   5.804%   $51.6006   $51.60   $51.60   $51.60  
  Purchase #7 $216.33   3.748%   $224.438   $224.44   $224.45   $224.40  
  7 purchase totals = $942.79       $997.7533   $997.75   $997.80   $997.70