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	$171.57	6.744%	$183.1407	$183.14	$183.15	$183.10
Purchase #2	$78.73	13.153%	$89.0854	$89.09	$89.10	$89.10
Purchase #3	$202.75	7.392%	$217.7373	$217.74	$217.75	$217.70
Purchase #4	$151.83	11.160%	$168.7742	$168.77	$168.75	$168.80
Purchase #5	$205.28	9.739%	$225.2722	$225.27	$225.25	$225.30
Purchase #6	$74.98	4.427%	$78.2994	$78.30	$78.30	$78.30
Purchase #7	$239.40	6.177%	$254.1877	$254.19	$254.20	$254.20
7 purchase totals =	$1,124.54		$1,216.4969	$1,216.50	$1,216.50	$1,216.50