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 $239.96   11.418%   $267.3586   $267.36   $267.35   $267.40  
  Purchase #2 $206.41   13.816%   $234.9276   $234.93   $234.95   $234.90  
  Purchase #3 $97.64   3.403%   $100.9627   $100.96   $100.95   $101.00  
  Purchase #4 $141.46   3.803%   $146.8397   $146.84   $146.85   $146.80  
  Purchase #5 $47.30   8.399%   $51.2727   $51.27   $51.25   $51.30  
  Purchase #6 $156.30   5.329%   $164.6292   $164.63   $164.65   $164.60  
  Purchase #7 $34.94   13.215%   $39.5573   $39.56   $39.55   $39.60  
  7 purchase totals = $924.01       $1,005.5478   $1,005.55   $1,005.55   $1,005.60