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 $118.41   4.737%   $124.0191   $124.02   $124.00   $124.00  
  Purchase #2 $176.80   5.373%   $186.2995   $186.30   $186.30   $186.30  
  Purchase #3 $64.37   3.467%   $66.6017   $66.60   $66.60   $66.60  
  Purchase #4 $43.65   9.866%   $47.9565   $47.96   $47.95   $48.00  
  Purchase #5 $125.95   13.122%   $142.4772   $142.48   $142.50   $142.50  
  Purchase #6 $65.47   10.560%   $72.3836   $72.38   $72.40   $72.40  
  Purchase #7 $50.99   7.408%   $54.7673   $54.77   $54.75   $54.80  
  7 purchase totals = $645.64       $694.5049   $694.51   $694.50   $694.60