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 $80.60   13.827%   $91.7446   $91.74   $91.75   $91.70  
  Purchase #2 $55.43   6.769%   $59.1821   $59.18   $59.20   $59.20  
  Purchase #3 $82.96   11.473%   $92.478   $92.48   $92.50   $92.50  
  Purchase #4 $220.79   10.545%   $244.0723   $244.07   $244.05   $244.10  
  Purchase #5 $172.47   13.408%   $195.5948   $195.59   $195.60   $195.60  
  Purchase #6 $20.89   5.338%   $22.0051   $22.01   $22.00   $22.00  
  Purchase #7 $193.48   13.385%   $219.3773   $219.38   $219.40   $219.40  
  7 purchase totals = $826.62       $924.4542   $924.45   $924.50   $924.50