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	$75.64	7.762%	$81.5112	$81.51	$81.50	$81.50
Purchase #2	$198.42	6.231%	$210.7836	$210.78	$210.80	$210.80
Purchase #3	$39.33	5.656%	$41.5545	$41.55	$41.55	$41.60
Purchase #4	$6.40	3.199%	$6.6047	$6.60	$6.60	$6.60
Purchase #5	$28.44	11.267%	$31.6443	$31.64	$31.65	$31.60
Purchase #6	$146.60	13.279%	$166.067	$166.07	$166.05	$166.10
Purchase #7	$122.56	3.811%	$127.2308	$127.23	$127.25	$127.20
7 purchase totals =	$617.39		$665.3961	$665.38	$665.40	$665.40