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 $185.92   7.121%   $199.1594   $199.16   $199.15   $199.20  
  Purchase #2 $158.82   11.291%   $176.7524   $176.75   $176.75   $176.80  
  Purchase #3 $90.86   5.783%   $96.1144   $96.11   $96.10   $96.10  
  Purchase #4 $87.25   13.435%   $98.972   $98.97   $98.95   $99.00  
  Purchase #5 $195.32   12.703%   $220.1315   $220.13   $220.15   $220.10  
  Purchase #6 $143.74   13.684%   $163.4094   $163.41   $163.40   $163.40  
  Purchase #7 $48.56   10.624%   $53.719   $53.72   $53.70   $53.70  
  7 purchase totals = $910.47       $1,008.2581   $1,008.25   $1,008.20   $1,008.30