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 $170.98   13.294%   $193.7101   $193.71   $193.70   $193.70  
  Purchase #2 $244.64   8.150%   $264.5782   $264.58   $264.60   $264.60  
  Purchase #3 $29.55   13.757%   $33.6152   $33.62   $33.60   $33.60  
  Purchase #4 $162.83   5.212%   $171.3167   $171.32   $171.30   $171.30  
  Purchase #5 $115.63   8.462%   $125.4146   $125.41   $125.40   $125.40  
  Purchase #6 $240.71   9.219%   $262.9011   $262.90   $262.90   $262.90  
  Purchase #7 $68.76   4.401%   $71.7861   $71.79   $71.80   $71.80  
  7 purchase totals = $1,033.10       $1,123.3220   $1,123.33   $1,123.30   $1,123.30