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	$123.64	5.788%	$130.7963	$130.80	$130.80	$130.80
Purchase #2	$95.28	6.114%	$101.1054	$101.11	$101.10	$101.10
Purchase #3	$52.40	12.866%	$59.1418	$59.14	$59.15	$59.10
Purchase #4	$227.45	4.786%	$238.3358	$238.34	$238.35	$238.30
Purchase #5	$44.73	5.782%	$47.3163	$47.32	$47.30	$47.30
Purchase #6	$99.28	10.211%	$109.4175	$109.42	$109.40	$109.40
Purchase #7	$99.43	12.373%	$111.7325	$111.73	$111.75	$111.70
7 purchase totals =	$742.21		$797.8456	$797.86	$797.85	$797.70