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 $238.80   10.853%   $264.717   $264.72   $264.70   $264.70  
  Purchase #2 $66.57   5.233%   $70.0536   $70.05   $70.05   $70.10  
  Purchase #3 $135.96   3.580%   $140.8274   $140.83   $140.85   $140.80  
  Purchase #4 $157.57   5.146%   $165.6786   $165.68   $165.70   $165.70  
  Purchase #5 $233.76   3.199%   $241.238   $241.24   $241.25   $241.20  
  Purchase #6 $30.49   12.758%   $34.3799   $34.38   $34.40   $34.40  
  Purchase #7 $240.40   4.691%   $251.6772   $251.68   $251.70   $251.70  
  7 purchase totals = $1,103.55       $1,168.5717   $1,168.58   $1,168.65   $1,168.60