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	$167.54	6.592%	$178.5842	$178.58	$178.60	$178.60
Purchase #2	$103.79	11.118%	$115.3294	$115.33	$115.35	$115.30
Purchase #3	$131.45	7.391%	$141.1655	$141.17	$141.15	$141.20
Purchase #4	$231.73	5.286%	$243.9792	$243.98	$244.00	$244.00
Purchase #5	$247.97	12.342%	$278.5745	$278.57	$278.55	$278.60
Purchase #6	$121.48	8.227%	$131.4742	$131.47	$131.45	$131.50
Purchase #7	$151.33	10.814%	$167.6948	$167.69	$167.70	$167.70
7 purchase totals =	$1,155.29		$1,256.8018	$1,256.79	$1,256.80	$1,256.90