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	$124.66	9.732%	$136.7919	$136.79	$136.80	$136.80
Purchase #2	$118.40	11.358%	$131.8479	$131.85	$131.85	$131.80
Purchase #3	$64.76	10.326%	$71.4471	$71.45	$71.45	$71.40
Purchase #4	$118.86	5.308%	$125.1691	$125.17	$125.15	$125.20
Purchase #5	$83.42	4.773%	$87.4016	$87.40	$87.40	$87.40
Purchase #6	$71.66	12.426%	$80.5645	$80.56	$80.55	$80.60
Purchase #7	$60.71	10.327%	$66.9795	$66.98	$67.00	$67.00
7 purchase totals =	$642.47		$700.2016	$700.20	$700.20	$700.20