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	$174.38	6.660%	$185.9937	$185.99	$186.00	$186.00
Purchase #2	$114.64	13.541%	$130.1634	$130.16	$130.15	$130.20
Purchase #3	$79.72	3.671%	$82.6465	$82.65	$82.65	$82.60
Purchase #4	$50.66	12.339%	$56.9109	$56.91	$56.90	$56.90
Purchase #5	$152.62	12.797%	$172.1508	$172.15	$172.15	$172.20
Purchase #6	$128.41	3.760%	$133.2382	$133.24	$133.25	$133.20
Purchase #7	$65.60	11.756%	$73.3119	$73.31	$73.30	$73.30
7 purchase totals =	$766.03		$834.4154	$834.41	$834.40	$834.40