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	$147.31	13.197%	$166.7505	$166.75	$166.75	$166.80
Purchase #2	$211.53	7.594%	$227.5936	$227.59	$227.60	$227.60
Purchase #3	$100.41	10.643%	$111.0966	$111.10	$111.10	$111.10
Purchase #4	$109.98	6.686%	$117.3333	$117.33	$117.35	$117.30
Purchase #5	$125.41	6.764%	$133.8927	$133.89	$133.90	$133.90
Purchase #6	$179.98	7.447%	$193.3831	$193.38	$193.40	$193.40
Purchase #7	$235.83	6.171%	$250.3831	$250.38	$250.40	$250.40
7 purchase totals =	$1,110.45		$1,200.4329	$1,200.42	$1,200.50	$1,200.50