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 $61.82   3.433%   $63.9423   $63.94   $63.95   $63.90  
  Purchase #2 $186.32   4.222%   $194.1864   $194.19   $194.20   $194.20  
  Purchase #3 $122.49   8.416%   $132.7988   $132.80   $132.80   $132.80  
  Purchase #4 $44.97   10.416%   $49.6541   $49.65   $49.65   $49.70  
  Purchase #5 $142.63   9.441%   $156.0957   $156.10   $156.10   $156.10  
  Purchase #6 $117.99   3.567%   $122.1987   $122.20   $122.20   $122.20  
  Purchase #7 $10.60   3.616%   $10.9833   $10.98   $11.00   $11.00  
  7 purchase totals = $686.82       $729.8593   $729.86   $729.90   $729.90