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	$200.54	4.838%	$210.2421	$210.24	$210.25	$210.20
Purchase #2	$248.33	4.239%	$258.8567	$258.86	$258.85	$258.90
Purchase #3	$129.63	8.379%	$140.4917	$140.49	$140.50	$140.50
Purchase #4	$33.38	11.248%	$37.1346	$37.13	$37.15	$37.10
Purchase #5	$229.54	4.680%	$240.2825	$240.28	$240.30	$240.30
Purchase #6	$175.72	5.735%	$185.7975	$185.80	$185.80	$185.80
Purchase #7	$76.42	9.651%	$83.7953	$83.80	$83.80	$83.80
7 purchase totals =	$1,093.56		$1,156.6004	$1,156.60	$1,156.65	$1,156.60