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 $24.44   7.793%   $26.3446   $26.34   $26.35   $26.30  
  Purchase #2 $193.72   11.465%   $215.93   $215.93   $215.95   $215.90  
  Purchase #3 $119.35   10.847%   $132.2959   $132.30   $132.30   $132.30  
  Purchase #4 $246.64   3.820%   $256.0616   $256.06   $256.05   $256.10  
  Purchase #5 $111.59   8.339%   $120.8955   $120.90   $120.90   $120.90  
  Purchase #6 $28.42   5.515%   $29.9874   $29.99   $30.00   $30.00  
  Purchase #7 $110.43   10.508%   $122.034   $122.03   $122.05   $122.00  
  7 purchase totals = $834.59       $903.5490   $903.55   $903.60   $903.50