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	$103.50	13.328%	$117.2945	$117.29	$117.30	$117.30
Purchase #2	$104.92	6.660%	$111.9077	$111.91	$111.90	$111.90
Purchase #3	$191.99	10.322%	$211.8072	$211.81	$211.80	$211.80
Purchase #4	$57.74	6.710%	$61.6144	$61.61	$61.60	$61.60
Purchase #5	$70.75	11.726%	$79.0461	$79.05	$79.05	$79.00
Purchase #6	$75.88	9.467%	$83.0636	$83.06	$83.05	$83.10
Purchase #7	$196.71	13.574%	$223.4114	$223.41	$223.40	$223.40
7 purchase totals =	$801.49		$888.1449	$888.14	$888.10	$888.10