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 $126.53   5.103%   $132.9868   $132.99   $133.00   $133.00  
  Purchase #2 $232.85   5.635%   $245.9711   $245.97   $245.95   $246.00  
  Purchase #3 $220.27   10.294%   $242.9446   $242.94   $242.95   $242.90  
  Purchase #4 $40.67   12.831%   $45.8884   $45.89   $45.90   $45.90  
  Purchase #5 $7.46   6.268%   $7.9276   $7.93   $7.95   $7.90  
  Purchase #6 $150.28   8.583%   $163.1785   $163.18   $163.20   $163.20  
  Purchase #7 $214.96   7.213%   $230.4651   $230.47   $230.45   $230.50  
  7 purchase totals = $993.02       $1,069.3621   $1,069.37   $1,069.40   $1,069.40