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	$123.48	6.541%	$131.5568	$131.56	$131.55	$131.60
Purchase #2	$235.40	7.316%	$252.6219	$252.62	$252.60	$252.60
Purchase #3	$20.46	6.842%	$21.8599	$21.86	$21.85	$21.90
Purchase #4	$112.31	5.505%	$118.4927	$118.49	$118.50	$118.50
Purchase #5	$6.86	4.434%	$7.1642	$7.16	$7.15	$7.20
Purchase #6	$61.71	11.565%	$68.8468	$68.85	$68.85	$68.80
Purchase #7	$199.80	11.430%	$222.6371	$222.64	$222.65	$222.60
7 purchase totals =	$760.02		$823.1794	$823.18	$823.15	$823.20