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 $104.91   9.176%   $114.5365   $114.54   $114.55   $114.50  
  Purchase #2 $133.48   10.796%   $147.8905   $147.89   $147.90   $147.90  
  Purchase #3 $214.38   7.140%   $229.6867   $229.69   $229.70   $229.70  
  Purchase #4 $74.84   8.281%   $81.0375   $81.04   $81.05   $81.00  
  Purchase #5 $14.32   10.776%   $15.8631   $15.86   $15.85   $15.90  
  Purchase #6 $58.33   3.124%   $60.1522   $60.15   $60.15   $60.20  
  Purchase #7 $131.96   4.851%   $138.3614   $138.36   $138.35   $138.40  
  7 purchase totals = $732.22       $787.5279   $787.53   $787.55   $787.60