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 $215.76   6.823%   $230.4813   $230.48   $230.50   $230.50  
  Purchase #2 $168.66   4.734%   $176.6444   $176.64   $176.65   $176.60  
  Purchase #3 $135.64   4.803%   $142.1548   $142.15   $142.15   $142.20  
  Purchase #4 $201.66   8.474%   $218.7487   $218.75   $218.75   $218.70  
  Purchase #5 $29.77   3.467%   $30.8021   $30.80   $30.80   $30.80  
  Purchase #6 $29.48   6.410%   $31.3697   $31.37   $31.35   $31.40  
  Purchase #7 $187.88   10.734%   $208.047   $208.05   $208.05   $208.00  
  7 purchase totals = $968.85       $1,038.2480   $1,038.24   $1,038.25   $1,038.20