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 $59.61   6.518%   $63.4954   $63.50   $63.50   $63.50  
  Purchase #2 $49.46   4.393%   $51.6328   $51.63   $51.65   $51.60  
  Purchase #3 $187.99   13.593%   $213.5435   $213.54   $213.55   $213.50  
  Purchase #4 $50.59   9.189%   $55.2387   $55.24   $55.25   $55.20  
  Purchase #5 $24.42   11.223%   $27.1607   $27.16   $27.15   $27.20  
  Purchase #6 $11.52   6.704%   $12.2923   $12.29   $12.30   $12.30  
  Purchase #7 $246.85   7.577%   $265.5538   $265.55   $265.55   $265.60  
  7 purchase totals = $630.44       $688.9172   $688.91   $688.95   $688.90