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 $58.92   6.174%   $62.5577   $62.56   $62.55   $62.60  
  Purchase #2 $184.75   10.221%   $203.6333   $203.63   $203.65   $203.60  
  Purchase #3 $250.72   8.254%   $271.4144   $271.41   $271.40   $271.40  
  Purchase #4 $167.69   10.694%   $185.6228   $185.62   $185.60   $185.60  
  Purchase #5 $131.58   6.475%   $140.0998   $140.10   $140.10   $140.10  
  Purchase #6 $9.50   10.673%   $10.5139   $10.51   $10.50   $10.50  
  Purchase #7 $13.49   10.823%   $14.95   $14.95   $14.95   $15.00  
  7 purchase totals = $816.65       $888.7919   $888.78   $888.75   $888.80