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 $208.65   7.646%   $224.6034   $224.60   $224.60   $224.60  
  Purchase #2 $36.88   3.202%   $38.0609   $38.06   $38.05   $38.10  
  Purchase #3 $102.87   9.803%   $112.9543   $112.95   $112.95   $113.00  
  Purchase #4 $238.54   11.848%   $266.8022   $266.80   $266.80   $266.80  
  Purchase #5 $232.38   9.145%   $253.6312   $253.63   $253.65   $253.60  
  Purchase #6 $76.38   9.631%   $83.7362   $83.74   $83.75   $83.70  
  Purchase #7 $15.33   8.377%   $16.6142   $16.61   $16.60   $16.60  
  7 purchase totals = $911.03       $996.4024   $996.39   $996.40   $996.40