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 $105.60   13.718%   $120.0862   $120.09   $120.10   $120.10  
  Purchase #2 $116.93   7.124%   $125.2601   $125.26   $125.25   $125.30  
  Purchase #3 $15.99   13.302%   $18.117   $18.12   $18.10   $18.10  
  Purchase #4 $174.53   4.252%   $181.951   $181.95   $181.95   $182.00  
  Purchase #5 $61.87   6.626%   $65.9695   $65.97   $65.95   $66.00  
  Purchase #6 $114.64   5.346%   $120.7687   $120.77   $120.75   $120.80  
  Purchase #7 $111.99   9.606%   $122.7478   $122.75   $122.75   $122.70  
  7 purchase totals = $701.55       $754.9003   $754.91   $754.85   $755.00