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 $54.57   12.473%   $61.3765   $61.38   $61.40   $61.40  
  Purchase #2 $43.90   4.673%   $45.9514   $45.95   $45.95   $46.00  
  Purchase #3 $250.89   10.501%   $277.236   $277.24   $277.25   $277.20  
  Purchase #4 $118.52   3.716%   $122.9242   $122.92   $122.90   $122.90  
  Purchase #5 $213.43   10.866%   $236.6213   $236.62   $236.60   $236.60  
  Purchase #6 $118.64   12.866%   $133.9042   $133.90   $133.90   $133.90  
  Purchase #7 $55.47   8.501%   $60.1855   $60.19   $60.20   $60.20  
  7 purchase totals = $855.42       $938.1991   $938.20   $938.20   $938.20