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 $184.70   7.676%   $198.8776   $198.88   $198.90   $198.90  
  Purchase #2 $223.25   4.378%   $233.0239   $233.02   $233.00   $233.00  
  Purchase #3 $23.82   11.706%   $26.6084   $26.61   $26.60   $26.60  
  Purchase #4 $32.92   13.724%   $37.4379   $37.44   $37.45   $37.40  
  Purchase #5 $61.51   7.845%   $66.3355   $66.34   $66.35   $66.30  
  Purchase #6 $221.47   11.845%   $247.7031   $247.70   $247.70   $247.70  
  Purchase #7 $207.32   3.352%   $214.2694   $214.27   $214.25   $214.30  
  7 purchase totals = $954.99       $1,024.2558   $1,024.26   $1,024.25   $1,024.20