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 $61.52   5.252%   $64.751   $64.75   $64.75   $64.80  
  Purchase #2 $11.83   3.826%   $12.2826   $12.28   $12.30   $12.30  
  Purchase #3 $7.83   11.710%   $8.7469   $8.75   $8.75   $8.70  
  Purchase #4 $109.36   13.361%   $123.9716   $123.97   $123.95   $124.00  
  Purchase #5 $246.34   8.542%   $267.3824   $267.38   $267.40   $267.40  
  Purchase #6 $213.87   12.121%   $239.7932   $239.79   $239.80   $239.80  
  Purchase #7 $92.91   13.465%   $105.4203   $105.42   $105.40   $105.40  
  7 purchase totals = $743.66       $822.3480   $822.34   $822.35   $822.40