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 $76.54   13.534%   $86.8989   $86.90   $86.90   $86.90  
  Purchase #2 $191.48   4.274%   $199.6639   $199.66   $199.65   $199.70  
  Purchase #3 $119.49   4.634%   $125.0272   $125.03   $125.05   $125.00  
  Purchase #4 $180.45   4.726%   $188.9781   $188.98   $189.00   $189.00  
  Purchase #5 $13.25   11.255%   $14.7413   $14.74   $14.75   $14.70  
  Purchase #6 $23.60   9.798%   $25.9123   $25.91   $25.90   $25.90  
  Purchase #7 $199.25   5.804%   $210.8145   $210.81   $210.80   $210.80  
  7 purchase totals = $804.06       $852.0362   $852.03   $852.05   $852.00