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	$74.59	3.522%	$77.2171	$77.22	$77.20	$77.20
Purchase #2	$84.61	9.273%	$92.4559	$92.46	$92.45	$92.50
Purchase #3	$218.45	7.841%	$235.5787	$235.58	$235.60	$235.60
Purchase #4	$188.86	9.264%	$206.356	$206.36	$206.35	$206.40
Purchase #5	$215.94	9.170%	$235.7417	$235.74	$235.75	$235.70
Purchase #6	$159.82	3.761%	$165.8308	$165.83	$165.85	$165.80
Purchase #7	$169.30	8.341%	$183.4213	$183.42	$183.40	$183.40
7 purchase totals =	$1,111.57		$1,196.6015	$1,196.61	$1,196.60	$1,196.60