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 $208.60   8.777%   $226.9088   $226.91   $226.90   $226.90  
  Purchase #2 $222.67   11.536%   $248.3572   $248.36   $248.35   $248.40  
  Purchase #3 $9.43   10.844%   $10.4526   $10.45   $10.45   $10.50  
  Purchase #4 $206.34   6.855%   $220.4846   $220.48   $220.50   $220.50  
  Purchase #5 $105.50   7.799%   $113.7279   $113.73   $113.75   $113.70  
  Purchase #6 $250.68   13.453%   $284.404   $284.40   $284.40   $284.40  
  Purchase #7 $217.64   9.701%   $238.7533   $238.75   $238.75   $238.80  
  7 purchase totals = $1,220.86       $1,343.0884   $1,343.08   $1,343.10   $1,343.20