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 $155.58   8.608%   $168.9723   $168.97   $168.95   $169.00  
  Purchase #2 $61.60   11.427%   $68.639   $68.64   $68.65   $68.60  
  Purchase #3 $241.66   13.468%   $274.2068   $274.21   $274.20   $274.20  
  Purchase #4 $90.88   6.182%   $96.4982   $96.50   $96.50   $96.50  
  Purchase #5 $28.47   3.825%   $29.559   $29.56   $29.55   $29.60  
  Purchase #6 $73.46   8.193%   $79.4786   $79.48   $79.50   $79.50  
  Purchase #7 $126.64   12.300%   $142.2167   $142.22   $142.20   $142.20  
  7 purchase totals = $778.29       $859.5706   $859.58   $859.55   $859.60