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	$80.39	3.144%	$82.9175	$82.92	$82.90	$82.90
Purchase #2	$101.29	7.801%	$109.1916	$109.19	$109.20	$109.20
Purchase #3	$99.82	3.462%	$103.2758	$103.28	$103.30	$103.30
Purchase #4	$210.79	4.191%	$219.6242	$219.62	$219.60	$219.60
Purchase #5	$114.36	13.590%	$129.9015	$129.90	$129.90	$129.90
Purchase #6	$46.45	9.413%	$50.8223	$50.82	$50.80	$50.80
Purchase #7	$231.45	11.610%	$258.3213	$258.32	$258.30	$258.30
7 purchase totals =	$884.55		$954.0542	$954.05	$954.00	$954.00