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 $233.45   8.372%   $252.9944   $252.99   $253.00   $253.00  
  Purchase #2 $75.65   10.571%   $83.647   $83.65   $83.65   $83.60  
  Purchase #3 $185.43   13.158%   $209.8289   $209.83   $209.85   $209.80  
  Purchase #4 $144.58   8.713%   $157.1773   $157.18   $157.20   $157.20  
  Purchase #5 $142.26   7.292%   $152.6336   $152.63   $152.65   $152.60  
  Purchase #6 $95.70   9.691%   $104.9743   $104.97   $104.95   $105.00  
  Purchase #7 $58.55   4.845%   $61.3867   $61.39   $61.40   $61.40  
  7 purchase totals = $935.62       $1,022.6422   $1,022.64   $1,022.70   $1,022.60