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 $242.62   7.462%   $260.7243   $260.72   $260.70   $260.70  
  Purchase #2 $22.48   10.728%   $24.8917   $24.89   $24.90   $24.90  
  Purchase #3 $192.74   12.211%   $216.2755   $216.28   $216.30   $216.30  
  Purchase #4 $233.36   8.574%   $253.3683   $253.37   $253.35   $253.40  
  Purchase #5 $225.67   7.591%   $242.8006   $242.80   $242.80   $242.80  
  Purchase #6 $64.34   4.477%   $67.2205   $67.22   $67.20   $67.20  
  Purchase #7 $155.85   9.179%   $170.1555   $170.16   $170.15   $170.20  
  7 purchase totals = $1,137.06       $1,235.4364   $1,235.44   $1,235.40   $1,235.50