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 $104.81   9.161%   $114.4116   $114.41   $114.40   $114.40  
  Purchase #2 $18.98   4.475%   $19.8294   $19.83   $19.85   $19.80  
  Purchase #3 $57.79   4.535%   $60.4108   $60.41   $60.40   $60.40  
  Purchase #4 $168.27   6.280%   $178.8374   $178.84   $178.85   $178.80  
  Purchase #5 $179.32   10.736%   $198.5718   $198.57   $198.55   $198.60  
  Purchase #6 $112.87   3.407%   $116.7155   $116.72   $116.70   $116.70  
  Purchase #7 $41.30   6.842%   $44.1257   $44.13   $44.15   $44.10  
  7 purchase totals = $683.34       $732.9022   $732.91   $732.90   $732.80