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	$159.91	3.184%	$165.0015	$165.00	$165.00	$165.00
Purchase #2	$77.69	6.202%	$82.5083	$82.51	$82.50	$82.50
Purchase #3	$57.34	4.516%	$59.9295	$59.93	$59.95	$59.90
Purchase #4	$226.42	6.640%	$241.4543	$241.45	$241.45	$241.50
Purchase #5	$173.99	3.471%	$180.0292	$180.03	$180.05	$180.00
Purchase #6	$217.59	10.638%	$240.7372	$240.74	$240.75	$240.70
Purchase #7	$57.75	4.744%	$60.4897	$60.49	$60.50	$60.50
7 purchase totals =	$970.69		$1,030.1497	$1,030.15	$1,030.20	$1,030.10