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	$248.76	4.606%	$260.2179	$260.22	$260.20	$260.20
Purchase #2	$195.77	11.426%	$218.1387	$218.14	$218.15	$218.10
Purchase #3	$229.29	6.662%	$244.5653	$244.57	$244.55	$244.60
Purchase #4	$125.46	6.368%	$133.4493	$133.45	$133.45	$133.40
Purchase #5	$38.89	9.106%	$42.4313	$42.43	$42.45	$42.40
Purchase #6	$204.47	10.727%	$226.4035	$226.40	$226.40	$226.40
Purchase #7	$86.60	4.288%	$90.3134	$90.31	$90.30	$90.30
7 purchase totals =	$1,129.24		$1,215.5194	$1,215.52	$1,215.50	$1,215.40