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 $64.43   7.154%   $69.0393   $69.04   $69.05   $69.00  
  Purchase #2 $107.86   13.622%   $122.5527   $122.55   $122.55   $122.60  
  Purchase #3 $175.46   13.744%   $199.5752   $199.58   $199.60   $199.60  
  Purchase #4 $60.76   8.466%   $65.9039   $65.90   $65.90   $65.90  
  Purchase #5 $181.96   13.707%   $206.9013   $206.90   $206.90   $206.90  
  Purchase #6 $92.67   6.232%   $98.4452   $98.45   $98.45   $98.40  
  Purchase #7 $190.51   12.572%   $214.4609   $214.46   $214.45   $214.50  
  7 purchase totals = $873.65       $976.8785   $976.88   $976.90   $976.90