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 $22.60   13.676%   $25.6908   $25.69   $25.70   $25.70  
  Purchase #2 $224.72   9.657%   $246.4212   $246.42   $246.40   $246.40  
  Purchase #3 $221.99   10.222%   $244.6818   $244.68   $244.70   $244.70  
  Purchase #4 $122.71   5.670%   $129.6677   $129.67   $129.65   $129.70  
  Purchase #5 $227.76   10.795%   $252.3467   $252.35   $252.35   $252.30  
  Purchase #6 $123.82   3.602%   $128.28   $128.28   $128.30   $128.30  
  Purchase #7 $6.28   4.679%   $6.5738   $6.57   $6.55   $6.60  
  7 purchase totals = $949.88       $1,033.6620   $1,033.66   $1,033.65   $1,033.70