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 $101.38   6.202%   $107.6676   $107.67   $107.65   $107.70  
  Purchase #2 $226.81   6.619%   $241.8226   $241.82   $241.80   $241.80  
  Purchase #3 $238.87   4.146%   $248.7736   $248.77   $248.75   $248.80  
  Purchase #4 $212.31   7.203%   $227.6027   $227.60   $227.60   $227.60  
  Purchase #5 $213.76   9.292%   $233.6226   $233.62   $233.60   $233.60  
  Purchase #6 $187.94   9.633%   $206.0443   $206.04   $206.05   $206.00  
  Purchase #7 $63.50   11.139%   $70.5733   $70.57   $70.55   $70.60  
  7 purchase totals = $1,244.57       $1,336.1067   $1,336.09   $1,336.00   $1,336.10