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 $68.45   11.578%   $76.3751   $76.38   $76.40   $76.40  
  Purchase #2 $104.76   9.149%   $114.3445   $114.34   $114.35   $114.30  
  Purchase #3 $31.27   11.251%   $34.7882   $34.79   $34.80   $34.80  
  Purchase #4 $126.50   10.465%   $139.7382   $139.74   $139.75   $139.70  
  Purchase #5 $236.77   10.309%   $261.1786   $261.18   $261.20   $261.20  
  Purchase #6 $240.38   11.226%   $267.3651   $267.37   $267.35   $267.40  
  Purchase #7 $155.65   13.320%   $176.3826   $176.38   $176.40   $176.40  
  7 purchase totals = $963.78       $1,070.1723   $1,070.18   $1,070.25   $1,070.20