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	$112.91	9.113%	$123.1995	$123.20	$123.20	$123.20
Purchase #2	$238.50	11.260%	$265.3551	$265.36	$265.35	$265.40
Purchase #3	$125.27	13.244%	$141.8608	$141.86	$141.85	$141.90
Purchase #4	$155.34	9.753%	$170.4903	$170.49	$170.50	$170.50
Purchase #5	$196.96	4.308%	$205.445	$205.45	$205.45	$205.40
Purchase #6	$229.94	13.628%	$261.2762	$261.28	$261.30	$261.30
Purchase #7	$212.45	9.749%	$233.1618	$233.16	$233.15	$233.20
7 purchase totals =	$1,271.37		$1,400.7887	$1,400.80	$1,400.80	$1,400.90