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 $66.38   9.564%   $72.7286   $72.73   $72.75   $72.70  
  Purchase #2 $188.53   5.802%   $199.4685   $199.47   $199.45   $199.50  
  Purchase #3 $34.38   7.111%   $36.8248   $36.82   $36.80   $36.80  
  Purchase #4 $50.44   4.769%   $52.8455   $52.85   $52.85   $52.80  
  Purchase #5 $72.90   8.605%   $79.173   $79.17   $79.15   $79.20  
  Purchase #6 $246.85   12.222%   $277.02   $277.02   $277.00   $277.00  
  Purchase #7 $155.43   13.552%   $176.4939   $176.49   $176.50   $176.50  
  7 purchase totals = $814.91       $894.5543   $894.55   $894.50   $894.50