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	$166.99	11.299%	$185.8582	$185.86	$185.85	$185.90
Purchase #2	$247.65	4.824%	$259.5966	$259.60	$259.60	$259.60
Purchase #3	$29.73	11.348%	$33.1038	$33.10	$33.10	$33.10
Purchase #4	$144.59	6.604%	$154.1387	$154.14	$154.15	$154.10
Purchase #5	$144.32	4.335%	$150.5763	$150.58	$150.60	$150.60
Purchase #6	$82.61	13.297%	$93.5947	$93.59	$93.60	$93.60
Purchase #7	$201.92	6.243%	$214.5259	$214.53	$214.55	$214.50
7 purchase totals =	$1,017.81		$1,091.3942	$1,091.40	$1,091.45	$1,091.40