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 $46.48   13.179%   $52.6056   $52.61   $52.60   $52.60  
  Purchase #2 $150.95   10.441%   $166.7107   $166.71   $166.70   $166.70  
  Purchase #3 $136.92   11.657%   $152.8808   $152.88   $152.90   $152.90  
  Purchase #4 $154.74   4.686%   $161.9911   $161.99   $162.00   $162.00  
  Purchase #5 $5.83   8.650%   $6.3343   $6.33   $6.35   $6.30  
  Purchase #6 $85.35   13.240%   $96.6503   $96.65   $96.65   $96.70  
  Purchase #7 $51.47   7.659%   $55.4121   $55.41   $55.40   $55.40  
  7 purchase totals = $631.74       $692.5849   $692.58   $692.60   $692.60