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 $86.98   5.406%   $91.6821   $91.68   $91.70   $91.70  
  Purchase #2 $209.39   4.767%   $219.3716   $219.37   $219.35   $219.40  
  Purchase #3 $24.78   8.435%   $26.8702   $26.87   $26.85   $26.90  
  Purchase #4 $250.73   4.778%   $262.7099   $262.71   $262.70   $262.70  
  Purchase #5 $213.69   5.414%   $225.2592   $225.26   $225.25   $225.30  
  Purchase #6 $6.65   8.547%   $7.2184   $7.22   $7.20   $7.20  
  Purchase #7 $83.56   3.573%   $86.5456   $86.55   $86.55   $86.50  
  7 purchase totals = $875.78       $919.6570   $919.66   $919.60   $919.70