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 $131.84   11.117%   $146.4967   $146.50   $146.50   $146.50  
  Purchase #2 $188.79   3.287%   $194.9955   $195.00   $195.00   $195.00  
  Purchase #3 $10.63   3.480%   $10.9999   $11.00   $11.00   $11.00  
  Purchase #4 $65.43   9.624%   $71.727   $71.73   $71.75   $71.70  
  Purchase #5 $130.82   11.655%   $146.0671   $146.07   $146.05   $146.10  
  Purchase #6 $144.43   11.706%   $161.337   $161.34   $161.35   $161.30  
  Purchase #7 $69.79   7.205%   $74.8184   $74.82   $74.80   $74.80  
  7 purchase totals = $741.73       $806.4416   $806.46   $806.45   $806.40