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	$92.38	11.840%	$103.3178	$103.32	$103.30	$103.30
Purchase #2	$23.74	8.744%	$25.8158	$25.82	$25.80	$25.80
Purchase #3	$106.67	4.781%	$111.7699	$111.77	$111.75	$111.80
Purchase #4	$229.57	9.427%	$251.2116	$251.21	$251.20	$251.20
Purchase #5	$242.39	8.314%	$262.5423	$262.54	$262.55	$262.50
Purchase #6	$101.84	9.751%	$111.7704	$111.77	$111.75	$111.80
Purchase #7	$41.92	9.153%	$45.7569	$45.76	$45.75	$45.80
7 purchase totals =	$838.51		$912.1847	$912.19	$912.10	$912.20