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	$133.96	3.858%	$139.1282	$139.13	$139.15	$139.10
Purchase #2	$148.59	9.178%	$162.2276	$162.23	$162.25	$162.20
Purchase #3	$73.47	12.169%	$82.4106	$82.41	$82.40	$82.40
Purchase #4	$137.91	10.374%	$152.2168	$152.22	$152.20	$152.20
Purchase #5	$116.92	12.676%	$131.7408	$131.74	$131.75	$131.70
Purchase #6	$172.79	6.194%	$183.4926	$183.49	$183.50	$183.50
Purchase #7	$116.62	10.223%	$128.5421	$128.54	$128.55	$128.50
7 purchase totals =	$900.26		$979.7587	$979.76	$979.80	$979.60