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 $93.78   4.478%   $97.9795   $97.98   $98.00   $98.00  
  Purchase #2 $31.26   10.673%   $34.5964   $34.60   $34.60   $34.60  
  Purchase #3 $15.37   7.180%   $16.4736   $16.47   $16.45   $16.50  
  Purchase #4 $172.66   6.195%   $183.3563   $183.36   $183.35   $183.40  
  Purchase #5 $180.69   7.306%   $193.8912   $193.89   $193.90   $193.90  
  Purchase #6 $168.34   13.754%   $191.4935   $191.49   $191.50   $191.50  
  Purchase #7 $65.99   11.281%   $73.4343   $73.43   $73.45   $73.40  
  7 purchase totals = $728.09       $791.2248   $791.22   $791.25   $791.30