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 $217.94   11.461%   $242.9181   $242.92   $242.90   $242.90  
  Purchase #2 $58.37   11.271%   $64.9489   $64.95   $64.95   $64.90  
  Purchase #3 $159.56   7.854%   $172.0918   $172.09   $172.10   $172.10  
  Purchase #4 $52.83   9.237%   $57.7099   $57.71   $57.70   $57.70  
  Purchase #5 $100.72   6.619%   $107.3867   $107.39   $107.40   $107.40  
  Purchase #6 $225.34   6.279%   $239.4891   $239.49   $239.50   $239.50  
  Purchase #7 $173.96   6.115%   $184.5977   $184.60   $184.60   $184.60  
  7 purchase totals = $988.72       $1,069.1422   $1,069.15   $1,069.15   $1,069.10