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 $228.47   12.751%   $257.6022   $257.60   $257.60   $257.60  
  Purchase #2 $214.70   4.318%   $223.9707   $223.97   $223.95   $224.00  
  Purchase #3 $109.38   13.114%   $123.7241   $123.72   $123.70   $123.70  
  Purchase #4 $181.77   6.584%   $193.7377   $193.74   $193.75   $193.70  
  Purchase #5 $23.68   3.389%   $24.4825   $24.48   $24.50   $24.50  
  Purchase #6 $204.83   8.363%   $221.9599   $221.96   $221.95   $222.00  
  Purchase #7 $190.97   5.718%   $201.8897   $201.89   $201.90   $201.90  
  7 purchase totals = $1,153.80       $1,247.3668   $1,247.36   $1,247.35   $1,247.40