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	$18.58	8.551%	$20.1688	$20.17	$20.15	$20.20
Purchase #2	$245.61	7.850%	$264.8904	$264.89	$264.90	$264.90
Purchase #3	$178.26	3.369%	$184.2656	$184.27	$184.25	$184.30
Purchase #4	$131.55	10.600%	$145.4943	$145.49	$145.50	$145.50
Purchase #5	$38.81	5.445%	$40.9232	$40.92	$40.90	$40.90
Purchase #6	$240.43	10.646%	$266.0262	$266.03	$266.05	$266.00
Purchase #7	$139.71	8.151%	$151.0978	$151.10	$151.10	$151.10
7 purchase totals =	$992.95		$1,072.8663	$1,072.87	$1,072.85	$1,072.90