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 $95.68   11.196%   $106.3923   $106.39   $106.40   $106.40  
  Purchase #2 $15.27   11.450%   $17.0184   $17.02   $17.00   $17.00  
  Purchase #3 $207.79   10.441%   $229.4854   $229.49   $229.50   $229.50  
  Purchase #4 $70.86   10.821%   $78.5278   $78.53   $78.55   $78.50  
  Purchase #5 $187.54   3.640%   $194.3665   $194.37   $194.35   $194.40  
  Purchase #6 $27.83   7.297%   $29.8608   $29.86   $29.85   $29.90  
  Purchase #7 $96.35   4.144%   $100.3427   $100.34   $100.35   $100.30  
  7 purchase totals = $701.32       $755.9939   $756.00   $756.00   $756.00