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 $23.50   10.465%   $25.9593   $25.96   $25.95   $26.00  
  Purchase #2 $176.81   7.559%   $190.1751   $190.18   $190.20   $190.20  
  Purchase #3 $27.61   8.649%   $29.998   $30.00   $30.00   $30.00  
  Purchase #4 $61.90   12.218%   $69.4629   $69.46   $69.45   $69.50  
  Purchase #5 $218.66   3.303%   $225.8823   $225.88   $225.90   $225.90  
  Purchase #6 $238.89   10.678%   $264.3987   $264.40   $264.40   $264.40  
  Purchase #7 $37.38   4.728%   $39.1473   $39.15   $39.15   $39.10  
  7 purchase totals = $784.75       $845.0236   $845.03   $845.05   $845.10