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 $86.43   13.852%   $98.4023   $98.40   $98.40   $98.40  
  Purchase #2 $167.86   4.373%   $175.2005   $175.20   $175.20   $175.20  
  Purchase #3 $79.97   3.289%   $82.6002   $82.60   $82.60   $82.60  
  Purchase #4 $44.72   4.654%   $46.8013   $46.80   $46.80   $46.80  
  Purchase #5 $30.91   12.526%   $34.7818   $34.78   $34.80   $34.80  
  Purchase #6 $8.89   7.263%   $9.5357   $9.54   $9.55   $9.50  
  Purchase #7 $235.38   11.389%   $262.1874   $262.19   $262.20   $262.20  
  7 purchase totals = $654.16       $709.5092   $709.51   $709.55   $709.50