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 $140.67   12.310%   $157.9865   $157.99   $158.00   $158.00  
  Purchase #2 $238.63   11.823%   $266.8432   $266.84   $266.85   $266.80  
  Purchase #3 $54.71   12.688%   $61.6516   $61.65   $61.65   $61.70  
  Purchase #4 $167.88   10.529%   $185.5561   $185.56   $185.55   $185.60  
  Purchase #5 $203.81   3.239%   $210.4114   $210.41   $210.40   $210.40  
  Purchase #6 $158.25   10.735%   $175.2381   $175.24   $175.25   $175.20  
  Purchase #7 $151.51   8.841%   $164.905   $164.91   $164.90   $164.90  
  7 purchase totals = $1,115.46       $1,222.5919   $1,222.60   $1,222.60   $1,222.60