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 $56.70   8.177%   $61.3364   $61.34   $61.35   $61.30  
  Purchase #2 $103.99   4.697%   $108.8744   $108.87   $108.85   $108.90  
  Purchase #3 $47.58   8.461%   $51.6057   $51.61   $51.60   $51.60  
  Purchase #4 $62.83   12.813%   $70.8804   $70.88   $70.90   $70.90  
  Purchase #5 $203.96   9.764%   $223.8747   $223.87   $223.85   $223.90  
  Purchase #6 $50.36   12.441%   $56.6253   $56.63   $56.65   $56.60  
  Purchase #7 $217.72   10.466%   $240.5066   $240.51   $240.50   $240.50  
  7 purchase totals = $743.14       $813.7035   $813.71   $813.70   $813.70