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 $147.82   4.830%   $154.9597   $154.96   $154.95   $155.00  
  Purchase #2 $38.46   8.226%   $41.6237   $41.62   $41.60   $41.60  
  Purchase #3 $245.29   4.449%   $256.203   $256.20   $256.20   $256.20  
  Purchase #4 $174.46   6.357%   $185.5504   $185.55   $185.55   $185.60  
  Purchase #5 $14.68   7.766%   $15.82   $15.82   $15.80   $15.80  
  Purchase #6 $15.28   8.270%   $16.5437   $16.54   $16.55   $16.50  
  Purchase #7 $156.92   3.202%   $161.9446   $161.94   $161.95   $161.90  
  7 purchase totals = $792.91       $832.6451   $832.63   $832.60   $832.60