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	$66.48	5.734%	$70.292	$70.29	$70.30	$70.30
Purchase #2	$158.94	4.391%	$165.9191	$165.92	$165.90	$165.90
Purchase #3	$73.90	9.200%	$80.6988	$80.70	$80.70	$80.70
Purchase #4	$83.75	5.220%	$88.1218	$88.12	$88.10	$88.10
Purchase #5	$95.32	8.524%	$103.4451	$103.45	$103.45	$103.40
Purchase #6	$151.52	9.816%	$166.3932	$166.39	$166.40	$166.40
Purchase #7	$19.44	4.331%	$20.2819	$20.28	$20.30	$20.30
7 purchase totals =	$649.35		$695.1519	$695.15	$695.15	$695.10