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 $182.49   10.646%   $201.9179   $201.92   $201.90   $201.90  
  Purchase #2 $241.34   4.154%   $251.3653   $251.37   $251.35   $251.40  
  Purchase #3 $72.77   6.501%   $77.5008   $77.50   $77.50   $77.50  
  Purchase #4 $17.36   6.726%   $18.5276   $18.53   $18.55   $18.50  
  Purchase #5 $83.63   10.264%   $92.2138   $92.21   $92.20   $92.20  
  Purchase #6 $216.87   12.830%   $244.6944   $244.69   $244.70   $244.70  
  Purchase #7 $139.73   8.565%   $151.6979   $151.70   $151.70   $151.70  
  7 purchase totals = $954.19       $1,037.9177   $1,037.92   $1,037.90   $1,037.90