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	$202.31	10.682%	$223.9208	$223.92	$223.90	$223.90
Purchase #2	$29.79	12.596%	$33.5423	$33.54	$33.55	$33.50
Purchase #3	$52.92	4.649%	$55.3803	$55.38	$55.40	$55.40
Purchase #4	$111.51	3.468%	$115.3772	$115.38	$115.40	$115.40
Purchase #5	$202.81	9.759%	$222.6022	$222.60	$222.60	$222.60
Purchase #6	$115.52	7.171%	$123.8039	$123.80	$123.80	$123.80
Purchase #7	$206.80	4.380%	$215.8578	$215.86	$215.85	$215.90
7 purchase totals =	$921.66		$990.4845	$990.48	$990.50	$990.50