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 $214.90   5.779%   $227.3191   $227.32   $227.30   $227.30  
  Purchase #2 $126.36   13.704%   $143.6764   $143.68   $143.70   $143.70  
  Purchase #3 $241.68   13.106%   $273.3546   $273.35   $273.35   $273.40  
  Purchase #4 $23.47   8.626%   $25.4945   $25.49   $25.50   $25.50  
  Purchase #5 $151.37   5.264%   $159.3381   $159.34   $159.35   $159.30  
  Purchase #6 $205.93   4.162%   $214.5008   $214.50   $214.50   $214.50  
  Purchase #7 $25.72   6.218%   $27.3193   $27.32   $27.30   $27.30  
  7 purchase totals = $989.43       $1,071.0028   $1,071.00   $1,071.00   $1,071.00