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 $216.89   10.790%   $240.2924   $240.29   $240.30   $240.30  
  Purchase #2 $235.38   8.292%   $254.8977   $254.90   $254.90   $254.90  
  Purchase #3 $140.73   8.701%   $152.9749   $152.97   $152.95   $153.00  
  Purchase #4 $25.30   4.374%   $26.4066   $26.41   $26.40   $26.40  
  Purchase #5 $124.26   4.782%   $130.2021   $130.20   $130.20   $130.20  
  Purchase #6 $140.30   6.855%   $149.9176   $149.92   $149.90   $149.90  
  Purchase #7 $27.92   6.745%   $29.8032   $29.80   $29.80   $29.80  
  7 purchase totals = $910.78       $984.4945   $984.49   $984.45   $984.50