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 $60.74   3.705%   $62.9904   $62.99   $63.00   $63.00  
  Purchase #2 $72.52   5.564%   $76.555   $76.56   $76.55   $76.60  
  Purchase #3 $168.61   11.718%   $188.3677   $188.37   $188.35   $188.40  
  Purchase #4 $73.71   3.276%   $76.1247   $76.12   $76.10   $76.10  
  Purchase #5 $16.84   13.402%   $19.0969   $19.10   $19.10   $19.10  
  Purchase #6 $167.87   9.585%   $183.9603   $183.96   $183.95   $184.00  
  Purchase #7 $26.54   3.425%   $27.449   $27.45   $27.45   $27.40  
  7 purchase totals = $586.83       $634.5440   $634.55   $634.50   $634.60