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 $83.54   9.456%   $91.4395   $91.44   $91.45   $91.40  
  Purchase #2 $188.79   4.377%   $197.0533   $197.05   $197.05   $197.10  
  Purchase #3 $190.73   12.506%   $214.5827   $214.58   $214.60   $214.60  
  Purchase #4 $71.30   7.563%   $76.6924   $76.69   $76.70   $76.70  
  Purchase #5 $165.45   12.370%   $185.9162   $185.92   $185.90   $185.90  
  Purchase #6 $180.56   5.211%   $189.969   $189.97   $189.95   $190.00  
  Purchase #7 $107.36   6.151%   $113.9637   $113.96   $113.95   $114.00  
  7 purchase totals = $987.73       $1,069.6168   $1,069.61   $1,069.60   $1,069.70