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	$174.79	12.200%	$196.1144	$196.11	$196.10	$196.10
Purchase #2	$90.47	6.766%	$96.5912	$96.59	$96.60	$96.60
Purchase #3	$181.42	10.273%	$200.0573	$200.06	$200.05	$200.10
Purchase #4	$115.52	8.491%	$125.3288	$125.33	$125.35	$125.30
Purchase #5	$240.45	13.662%	$273.3003	$273.30	$273.30	$273.30
Purchase #6	$151.28	10.643%	$167.3807	$167.38	$167.40	$167.40
Purchase #7	$210.63	4.483%	$220.0725	$220.07	$220.05	$220.10
7 purchase totals =	$1,164.56		$1,278.8452	$1,278.84	$1,278.85	$1,278.90