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 $148.35   10.674%   $164.1849   $164.18   $164.20   $164.20  
  Purchase #2 $97.63   4.797%   $102.3133   $102.31   $102.30   $102.30  
  Purchase #3 $192.89   7.159%   $206.699   $206.70   $206.70   $206.70  
  Purchase #4 $231.43   13.635%   $262.9855   $262.99   $263.00   $263.00  
  Purchase #5 $116.62   3.619%   $120.8405   $120.84   $120.85   $120.80  
  Purchase #6 $70.66   8.269%   $76.5029   $76.50   $76.50   $76.50  
  Purchase #7 $237.30   13.678%   $269.7579   $269.76   $269.75   $269.80  
  7 purchase totals = $1,094.88       $1,203.2840   $1,203.28   $1,203.30   $1,203.30