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	$150.39	13.130%	$170.1362	$170.14	$170.15	$170.10
Purchase #2	$107.26	8.464%	$116.3385	$116.34	$116.35	$116.30
Purchase #3	$68.97	3.789%	$71.5833	$71.58	$71.60	$71.60
Purchase #4	$99.77	4.380%	$104.1399	$104.14	$104.15	$104.10
Purchase #5	$104.31	11.738%	$116.5539	$116.55	$116.55	$116.60
Purchase #6	$116.74	9.490%	$127.8186	$127.82	$127.80	$127.80
Purchase #7	$110.28	4.562%	$115.311	$115.31	$115.30	$115.30
7 purchase totals =	$757.72		$821.8814	$821.88	$821.90	$821.80