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	$176.46	3.706%	$182.9996	$183.00	$183.00	$183.00
Purchase #2	$154.55	10.846%	$171.3125	$171.31	$171.30	$171.30
Purchase #3	$218.55	9.228%	$238.7178	$238.72	$238.70	$238.70
Purchase #4	$10.36	3.224%	$10.694	$10.69	$10.70	$10.70
Purchase #5	$149.67	11.433%	$166.7818	$166.78	$166.80	$166.80
Purchase #6	$90.69	9.856%	$99.6284	$99.63	$99.65	$99.60
Purchase #7	$106.64	4.352%	$111.281	$111.28	$111.30	$111.30
7 purchase totals =	$906.92		$981.4151	$981.41	$981.45	$981.40