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 $232.51   9.680%   $255.017   $255.02   $255.00   $255.00  
  Purchase #2 $60.49   3.148%   $62.3942   $62.39   $62.40   $62.40  
  Purchase #3 $149.43   9.131%   $163.0745   $163.07   $163.05   $163.10  
  Purchase #4 $161.54   10.821%   $179.0202   $179.02   $179.00   $179.00  
  Purchase #5 $221.43   11.463%   $246.8125   $246.81   $246.80   $246.80  
  Purchase #6 $129.50   6.543%   $137.9732   $137.97   $137.95   $138.00  
  Purchase #7 $206.84   7.253%   $221.8421   $221.84   $221.85   $221.80  
  7 purchase totals = $1,161.74       $1,266.1337   $1,266.12   $1,266.05   $1,266.10