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 $204.62   10.303%   $225.702   $225.70   $225.70   $225.70  
  Purchase #2 $124.96   4.360%   $130.4083   $130.41   $130.40   $130.40  
  Purchase #3 $55.73   3.496%   $57.6783   $57.68   $57.70   $57.70  
  Purchase #4 $35.35   3.701%   $36.6583   $36.66   $36.65   $36.70  
  Purchase #5 $10.57   6.683%   $11.2764   $11.28   $11.30   $11.30  
  Purchase #6 $29.46   4.365%   $30.7459   $30.75   $30.75   $30.70  
  Purchase #7 $226.84   9.761%   $248.9819   $248.98   $249.00   $249.00  
  7 purchase totals = $687.53       $741.4511   $741.46   $741.50   $741.50