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 $65.82   12.311%   $73.9231   $73.92   $73.90   $73.90  
  Purchase #2 $23.90   10.183%   $26.3337   $26.33   $26.35   $26.30  
  Purchase #3 $207.40   13.818%   $236.0585   $236.06   $236.05   $236.10  
  Purchase #4 $107.58   9.459%   $117.756   $117.76   $117.75   $117.80  
  Purchase #5 $220.81   12.470%   $248.345   $248.35   $248.35   $248.30  
  Purchase #6 $98.30   11.582%   $109.6851   $109.69   $109.70   $109.70  
  Purchase #7 $159.68   6.373%   $169.8564   $169.86   $169.85   $169.90  
  7 purchase totals = $883.49       $981.9578   $981.97   $981.95   $982.00