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 $93.63   4.772%   $98.098   $98.10   $98.10   $98.10  
  Purchase #2 $50.39   11.408%   $56.1385   $56.14   $56.15   $56.10  
  Purchase #3 $34.97   4.340%   $36.4877   $36.49   $36.50   $36.50  
  Purchase #4 $238.61   10.570%   $263.8311   $263.83   $263.85   $263.80  
  Purchase #5 $159.33   11.860%   $178.2265   $178.23   $178.25   $178.20  
  Purchase #6 $184.34   3.129%   $190.108   $190.11   $190.10   $190.10  
  Purchase #7 $27.57   8.235%   $29.8404   $29.84   $29.85   $29.80  
  7 purchase totals = $788.84       $852.7302   $852.74   $852.80   $852.60