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	$155.50	3.705%	$161.2613	$161.26	$161.25	$161.30
Purchase #2	$53.50	5.736%	$56.5688	$56.57	$56.55	$56.60
Purchase #3	$214.68	13.611%	$243.9001	$243.90	$243.90	$243.90
Purchase #4	$40.97	3.521%	$42.4126	$42.41	$42.40	$42.40
Purchase #5	$111.63	7.647%	$120.1663	$120.17	$120.15	$120.20
Purchase #6	$56.40	5.537%	$59.5229	$59.52	$59.50	$59.50
Purchase #7	$89.87	5.449%	$94.767	$94.77	$94.75	$94.80
7 purchase totals =	$722.55		$778.5990	$778.60	$778.50	$778.70