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 $209.77   10.553%   $231.907   $231.91   $231.90   $231.90  
  Purchase #2 $74.29   10.177%   $81.8505   $81.85   $81.85   $81.90  
  Purchase #3 $247.43   4.362%   $258.2229   $258.22   $258.20   $258.20  
  Purchase #4 $63.47   3.598%   $65.7537   $65.75   $65.75   $65.80  
  Purchase #5 $106.86   7.379%   $114.7452   $114.75   $114.75   $114.70  
  Purchase #6 $71.90   3.468%   $74.3935   $74.39   $74.40   $74.40  
  Purchase #7 $176.82   13.126%   $200.0294   $200.03   $200.05   $200.00  
  7 purchase totals = $950.54       $1,026.9022   $1,026.90   $1,026.90   $1,026.90