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 $111.82   11.333%   $124.4926   $124.49   $124.50   $124.50  
  Purchase #2 $185.83   7.623%   $199.9958   $200.00   $200.00   $200.00  
  Purchase #3 $205.95   12.672%   $232.048   $232.05   $232.05   $232.00  
  Purchase #4 $86.32   4.211%   $89.9549   $89.95   $89.95   $90.00  
  Purchase #5 $210.78   9.353%   $230.4943   $230.49   $230.50   $230.50  
  Purchase #6 $84.84   8.271%   $91.8571   $91.86   $91.85   $91.90  
  Purchase #7 $95.47   7.505%   $102.635   $102.64   $102.65   $102.60  
  7 purchase totals = $981.01       $1,071.4777   $1,071.48   $1,071.50   $1,071.50