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 $93.95   4.853%   $98.5094   $98.51   $98.50   $98.50  
  Purchase #2 $53.33   3.448%   $55.1688   $55.17   $55.15   $55.20  
  Purchase #3 $85.41   10.488%   $94.3678   $94.37   $94.35   $94.40  
  Purchase #4 $77.95   7.623%   $83.8921   $83.89   $83.90   $83.90  
  Purchase #5 $207.63   7.719%   $223.657   $223.66   $223.65   $223.70  
  Purchase #6 $106.27   10.113%   $117.0171   $117.02   $117.00   $117.00  
  Purchase #7 $20.74   9.463%   $22.7026   $22.70   $22.70   $22.70  
  7 purchase totals = $645.28       $695.3148   $695.32   $695.25   $695.40