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	$81.25	10.146%	$89.4936	$89.49	$89.50	$89.50
Purchase #2	$180.52	11.257%	$200.8411	$200.84	$200.85	$200.80
Purchase #3	$122.78	9.801%	$134.8137	$134.81	$134.80	$134.80
Purchase #4	$168.26	3.451%	$174.0667	$174.07	$174.05	$174.10
Purchase #5	$135.80	3.755%	$140.8993	$140.90	$140.90	$140.90
Purchase #6	$223.31	13.309%	$253.0303	$253.03	$253.05	$253.00
Purchase #7	$147.81	7.459%	$158.8351	$158.84	$158.85	$158.80
7 purchase totals =	$1,059.73		$1,151.9798	$1,151.98	$1,152.00	$1,151.90