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	$247.67	8.339%	$268.3232	$268.32	$268.30	$268.30
Purchase #2	$89.32	11.305%	$99.4176	$99.42	$99.40	$99.40
Purchase #3	$182.87	3.423%	$189.1296	$189.13	$189.15	$189.10
Purchase #4	$211.85	10.345%	$233.7659	$233.77	$233.75	$233.80
Purchase #5	$56.68	10.666%	$62.7255	$62.73	$62.75	$62.70
Purchase #6	$12.85	8.194%	$13.9029	$13.90	$13.90	$13.90
Purchase #7	$47.41	7.123%	$50.787	$50.79	$50.80	$50.80
7 purchase totals =	$848.65		$918.0517	$918.06	$918.05	$918.00