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	$32.77	3.189%	$33.815	$33.82	$33.80	$33.80
Purchase #2	$114.77	12.341%	$128.9338	$128.93	$128.95	$128.90
Purchase #3	$227.96	13.659%	$259.0971	$259.10	$259.10	$259.10
Purchase #4	$191.42	13.647%	$217.5431	$217.54	$217.55	$217.50
Purchase #5	$83.75	5.153%	$88.0656	$88.07	$88.05	$88.10
Purchase #6	$147.43	3.276%	$152.2598	$152.26	$152.25	$152.30
Purchase #7	$194.41	13.496%	$220.6476	$220.65	$220.65	$220.60
7 purchase totals =	$992.51		$1,100.3620	$1,100.37	$1,100.35	$1,100.30