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 $93.77   3.352%   $96.9132   $96.91   $96.90   $96.90  
  Purchase #2 $157.67   3.519%   $163.2184   $163.22   $163.20   $163.20  
  Purchase #3 $203.32   8.108%   $219.8052   $219.81   $219.80   $219.80  
  Purchase #4 $147.39   10.171%   $162.381   $162.38   $162.40   $162.40  
  Purchase #5 $108.98   5.295%   $114.7505   $114.75   $114.75   $114.80  
  Purchase #6 $123.72   8.363%   $134.0667   $134.07   $134.05   $134.10  
  Purchase #7 $57.88   6.661%   $61.7354   $61.74   $61.75   $61.70  
  7 purchase totals = $892.73       $952.8704   $952.88   $952.85   $952.90