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 $212.84   6.477%   $226.6256   $226.63   $226.65   $226.60  
  Purchase #2 $182.64   8.799%   $198.7105   $198.71   $198.70   $198.70  
  Purchase #3 $179.59   5.514%   $189.4926   $189.49   $189.50   $189.50  
  Purchase #4 $222.39   10.547%   $245.8455   $245.85   $245.85   $245.80  
  Purchase #5 $84.75   7.394%   $91.0164   $91.02   $91.00   $91.00  
  Purchase #6 $36.32   13.472%   $41.213   $41.21   $41.20   $41.20  
  Purchase #7 $200.41   6.507%   $213.4507   $213.45   $213.45   $213.50  
  7 purchase totals = $1,118.94       $1,206.3543   $1,206.36   $1,206.35   $1,206.30