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 $114.62   8.848%   $124.7616   $124.76   $124.75   $124.80  
  Purchase #2 $208.77   10.491%   $230.6721   $230.67   $230.65   $230.70  
  Purchase #3 $171.90   13.596%   $195.2715   $195.27   $195.25   $195.30  
  Purchase #4 $108.29   6.674%   $115.5173   $115.52   $115.50   $115.50  
  Purchase #5 $41.72   4.475%   $43.587   $43.59   $43.60   $43.60  
  Purchase #6 $115.98   11.782%   $129.6448   $129.64   $129.65   $129.60  
  Purchase #7 $134.84   10.505%   $149.0049   $149.00   $149.00   $149.00  
  7 purchase totals = $896.12       $988.4592   $988.45   $988.40   $988.50