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 $57.59   4.432%   $60.1424   $60.14   $60.15   $60.10  
  Purchase #2 $192.53   8.327%   $208.562   $208.56   $208.55   $208.60  
  Purchase #3 $108.79   5.787%   $115.0857   $115.09   $115.10   $115.10  
  Purchase #4 $185.30   13.382%   $210.0968   $210.10   $210.10   $210.10  
  Purchase #5 $149.38   8.865%   $162.6225   $162.62   $162.60   $162.60  
  Purchase #6 $211.41   4.612%   $221.1602   $221.16   $221.15   $221.20  
  Purchase #7 $40.77   12.201%   $45.7443   $45.74   $45.75   $45.70  
  7 purchase totals = $945.77       $1,023.4139   $1,023.41   $1,023.40   $1,023.40