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 $116.87   5.512%   $123.3119   $123.31   $123.30   $123.30  
  Purchase #2 $189.96   8.235%   $205.6032   $205.60   $205.60   $205.60  
  Purchase #3 $156.43   6.299%   $166.2835   $166.28   $166.30   $166.30  
  Purchase #4 $241.63   6.616%   $257.6162   $257.62   $257.60   $257.60  
  Purchase #5 $157.26   11.593%   $175.4912   $175.49   $175.50   $175.50  
  Purchase #6 $227.58   4.221%   $237.1862   $237.19   $237.20   $237.20  
  Purchase #7 $192.70   6.625%   $205.4664   $205.47   $205.45   $205.50  
  7 purchase totals = $1,282.43       $1,370.9586   $1,370.96   $1,370.95   $1,371.00