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 $245.83   11.767%   $274.7568   $274.76   $274.75   $274.80  
  Purchase #2 $157.76   7.603%   $169.7545   $169.75   $169.75   $169.80  
  Purchase #3 $154.93   4.378%   $161.7128   $161.71   $161.70   $161.70  
  Purchase #4 $116.43   12.803%   $131.3365   $131.34   $131.35   $131.30  
  Purchase #5 $198.55   8.164%   $214.7596   $214.76   $214.75   $214.80  
  Purchase #6 $218.49   10.629%   $241.7133   $241.71   $241.70   $241.70  
  Purchase #7 $234.29   12.470%   $263.506   $263.51   $263.50   $263.50  
  7 purchase totals = $1,326.28       $1,457.5395   $1,457.54   $1,457.50   $1,457.60