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 $249.90   13.223%   $282.9443   $282.94   $282.95   $282.90  
  Purchase #2 $23.94   7.292%   $25.6857   $25.69   $25.70   $25.70  
  Purchase #3 $193.86   7.275%   $207.9633   $207.96   $207.95   $208.00  
  Purchase #4 $219.40   6.329%   $233.2858   $233.29   $233.30   $233.30  
  Purchase #5 $130.51   13.297%   $147.8639   $147.86   $147.85   $147.90  
  Purchase #6 $18.76   13.779%   $21.3449   $21.34   $21.35   $21.30  
  Purchase #7 $100.63   3.776%   $104.4298   $104.43   $104.45   $104.40  
  7 purchase totals = $937.00       $1,023.5177   $1,023.51   $1,023.55   $1,023.50