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	$180.58	4.621%	$188.9246	$188.92	$188.90	$188.90
Purchase #2	$157.30	10.314%	$173.5239	$173.52	$173.50	$173.50
Purchase #3	$84.62	5.438%	$89.2216	$89.22	$89.20	$89.20
Purchase #4	$125.66	13.755%	$142.9445	$142.94	$142.95	$142.90
Purchase #5	$54.58	9.246%	$59.6265	$59.63	$59.65	$59.60
Purchase #6	$31.62	9.861%	$34.738	$34.74	$34.75	$34.70
Purchase #7	$105.42	7.151%	$112.9586	$112.96	$112.95	$113.00
7 purchase totals =	$739.78		$801.9377	$801.93	$801.90	$801.80