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 $61.43   12.147%   $68.8919   $68.89   $68.90   $68.90  
  Purchase #2 $182.95   7.469%   $196.6145   $196.61   $196.60   $196.60  
  Purchase #3 $113.45   3.341%   $117.2404   $117.24   $117.25   $117.20  
  Purchase #4 $103.37   10.728%   $114.4595   $114.46   $114.45   $114.50  
  Purchase #5 $12.68   10.663%   $14.0321   $14.03   $14.05   $14.00  
  Purchase #6 $219.97   12.149%   $246.6942   $246.69   $246.70   $246.70  
  Purchase #7 $141.30   12.240%   $158.5951   $158.60   $158.60   $158.60  
  7 purchase totals = $835.15       $916.5277   $916.52   $916.55   $916.50