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	$156.45	9.275%	$170.9607	$170.96	$170.95	$171.00
Purchase #2	$131.45	11.745%	$146.8888	$146.89	$146.90	$146.90
Purchase #3	$134.67	12.202%	$151.1024	$151.10	$151.10	$151.10
Purchase #4	$210.46	10.779%	$233.1455	$233.15	$233.15	$233.10
Purchase #5	$133.55	10.854%	$148.0455	$148.05	$148.05	$148.00
Purchase #6	$221.96	6.577%	$236.5583	$236.56	$236.55	$236.60
Purchase #7	$73.68	13.265%	$83.4537	$83.45	$83.45	$83.50
7 purchase totals =	$1,062.22		$1,170.1549	$1,170.16	$1,170.15	$1,170.20