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	$36.55	8.204%	$39.5486	$39.55	$39.55	$39.50
Purchase #2	$158.52	5.340%	$166.985	$166.99	$167.00	$167.00
Purchase #3	$135.65	11.511%	$151.2647	$151.26	$151.25	$151.30
Purchase #4	$112.50	9.799%	$123.5239	$123.52	$123.50	$123.50
Purchase #5	$246.70	11.744%	$275.6724	$275.67	$275.65	$275.70
Purchase #6	$115.92	12.415%	$130.3115	$130.31	$130.30	$130.30
Purchase #7	$185.58	13.288%	$210.2399	$210.24	$210.25	$210.20
7 purchase totals =	$991.42		$1,097.5460	$1,097.54	$1,097.50	$1,097.50