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	$127.35	3.361%	$131.6302	$131.63	$131.65	$131.60
Purchase #2	$40.41	9.377%	$44.1992	$44.20	$44.20	$44.20
Purchase #3	$236.62	4.723%	$247.7956	$247.80	$247.80	$247.80
Purchase #4	$95.84	4.726%	$100.3694	$100.37	$100.35	$100.40
Purchase #5	$36.85	10.773%	$40.8199	$40.82	$40.80	$40.80
Purchase #6	$157.70	10.487%	$174.238	$174.24	$174.25	$174.20
Purchase #7	$170.60	8.536%	$185.1624	$185.16	$185.15	$185.20
7 purchase totals =	$865.37		$924.2147	$924.22	$924.20	$924.20