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 $132.78   5.380%   $139.9236   $139.92   $139.90   $139.90  
  Purchase #2 $47.62   11.394%   $53.0458   $53.05   $53.05   $53.00  
  Purchase #3 $81.91   8.668%   $89.01   $89.01   $89.00   $89.00  
  Purchase #4 $10.62   10.151%   $11.698   $11.70   $11.70   $11.70  
  Purchase #5 $14.75   10.201%   $16.2546   $16.25   $16.25   $16.30  
  Purchase #6 $30.35   10.335%   $33.4867   $33.49   $33.50   $33.50  
  Purchase #7 $80.98   7.725%   $87.2357   $87.24   $87.25   $87.20  
  7 purchase totals = $399.01       $430.6544   $430.66   $430.65   $430.60