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 $129.35   9.686%   $141.8788   $141.88   $141.90   $141.90  
  Purchase #2 $214.34   4.801%   $224.6305   $224.63   $224.65   $224.60  
  Purchase #3 $49.32   11.847%   $55.1629   $55.16   $55.15   $55.20  
  Purchase #4 $227.90   9.172%   $248.803   $248.80   $248.80   $248.80  
  Purchase #5 $102.37   13.340%   $116.0262   $116.03   $116.05   $116.00  
  Purchase #6 $87.77   12.594%   $98.8238   $98.82   $98.80   $98.80  
  Purchase #7 $162.87   7.195%   $174.5885   $174.59   $174.60   $174.60  
  7 purchase totals = $973.92       $1,059.9137   $1,059.91   $1,059.95   $1,059.90