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 $241.35   6.166%   $256.2316   $256.23   $256.25   $256.20  
  Purchase #2 $43.97   3.355%   $45.4452   $45.45   $45.45   $45.40  
  Purchase #3 $153.51   6.624%   $163.6785   $163.68   $163.70   $163.70  
  Purchase #4 $168.35   9.581%   $184.4796   $184.48   $184.50   $184.50  
  Purchase #5 $238.38   13.128%   $269.6745   $269.67   $269.65   $269.70  
  Purchase #6 $234.65   8.660%   $254.9707   $254.97   $254.95   $255.00  
  Purchase #7 $94.63   7.661%   $101.8796   $101.88   $101.90   $101.90  
  7 purchase totals = $1,174.84       $1,276.3597   $1,276.36   $1,276.40   $1,276.40