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 $119.68   3.371%   $123.7144   $123.71   $123.70   $123.70  
  Purchase #2 $15.76   6.832%   $16.8367   $16.84   $16.85   $16.80  
  Purchase #3 $225.30   7.217%   $241.5599   $241.56   $241.55   $241.60  
  Purchase #4 $236.74   9.271%   $258.6882   $258.69   $258.70   $258.70  
  Purchase #5 $245.51   12.263%   $275.6169   $275.62   $275.60   $275.60  
  Purchase #6 $12.59   12.288%   $14.1371   $14.14   $14.15   $14.10  
  Purchase #7 $70.58   8.161%   $76.34   $76.34   $76.35   $76.30  
  7 purchase totals = $926.16       $1,006.8932   $1,006.90   $1,006.90   $1,006.80