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	$30.55	6.130%	$32.4227	$32.42	$32.40	$32.40
Purchase #2	$249.60	4.686%	$261.2963	$261.30	$261.30	$261.30
Purchase #3	$108.93	5.413%	$114.8264	$114.83	$114.85	$114.80
Purchase #4	$153.34	4.234%	$159.8324	$159.83	$159.85	$159.80
Purchase #5	$89.69	3.222%	$92.5798	$92.58	$92.60	$92.60
Purchase #6	$101.59	7.865%	$109.5801	$109.58	$109.60	$109.60
Purchase #7	$182.76	12.636%	$205.8536	$205.85	$205.85	$205.90
7 purchase totals =	$916.46		$976.3913	$976.39	$976.45	$976.40