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	$173.34	4.243%	$180.6948	$180.69	$180.70	$180.70
Purchase #2	$82.75	9.689%	$90.7676	$90.77	$90.75	$90.80
Purchase #3	$185.57	10.718%	$205.4594	$205.46	$205.45	$205.50
Purchase #4	$84.51	6.680%	$90.1553	$90.16	$90.15	$90.20
Purchase #5	$151.67	6.245%	$161.1418	$161.14	$161.15	$161.10
Purchase #6	$124.85	3.561%	$129.2959	$129.30	$129.30	$129.30
Purchase #7	$131.93	8.311%	$142.8947	$142.89	$142.90	$142.90
7 purchase totals =	$934.62		$1,000.4095	$1,000.41	$1,000.40	$1,000.50