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 $62.60   10.159%   $68.9595   $68.96   $68.95   $69.00  
  Purchase #2 $118.66   7.433%   $127.48   $127.48   $127.50   $127.50  
  Purchase #3 $219.66   3.163%   $226.6078   $226.61   $226.60   $226.60  
  Purchase #4 $167.70   13.657%   $190.6028   $190.60   $190.60   $190.60  
  Purchase #5 $125.58   8.671%   $136.469   $136.47   $136.45   $136.50  
  Purchase #6 $74.31   6.177%   $78.9001   $78.90   $78.90   $78.90  
  Purchase #7 $25.97   8.783%   $28.2509   $28.25   $28.25   $28.30  
  7 purchase totals = $794.48       $857.2701   $857.27   $857.25   $857.40