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 $248.42   8.460%   $269.4363   $269.44   $269.45   $269.40  
  Purchase #2 $234.96   3.580%   $243.3716   $243.37   $243.35   $243.40  
  Purchase #3 $103.83   9.792%   $113.997   $114.00   $114.00   $114.00  
  Purchase #4 $57.62   4.525%   $60.2273   $60.23   $60.25   $60.20  
  Purchase #5 $105.84   10.415%   $116.8632   $116.86   $116.85   $116.90  
  Purchase #6 $146.39   12.320%   $164.4252   $164.43   $164.45   $164.40  
  Purchase #7 $187.85   10.366%   $207.3225   $207.32   $207.30   $207.30  
  7 purchase totals = $1,084.91       $1,175.6431   $1,175.65   $1,175.65   $1,175.60