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 $211.29   10.797%   $234.103   $234.10   $234.10   $234.10  
  Purchase #2 $113.93   10.631%   $126.0419   $126.04   $126.05   $126.00  
  Purchase #3 $66.77   4.815%   $69.985   $69.99   $70.00   $70.00  
  Purchase #4 $244.48   8.766%   $265.9111   $265.91   $265.90   $265.90  
  Purchase #5 $227.91   13.138%   $257.8528   $257.85   $257.85   $257.90  
  Purchase #6 $123.46   6.510%   $131.4972   $131.50   $131.50   $131.50  
  Purchase #7 $217.93   10.585%   $240.9979   $241.00   $241.00   $241.00  
  7 purchase totals = $1,205.77       $1,326.3889   $1,326.39   $1,326.40   $1,326.40