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	$177.89	4.549%	$185.9822	$185.98	$186.00	$186.00
Purchase #2	$221.33	8.566%	$240.2891	$240.29	$240.30	$240.30
Purchase #3	$156.60	7.173%	$167.8329	$167.83	$167.85	$167.80
Purchase #4	$101.85	13.729%	$115.833	$115.83	$115.85	$115.80
Purchase #5	$38.79	12.450%	$43.6194	$43.62	$43.60	$43.60
Purchase #6	$202.65	8.786%	$220.4548	$220.45	$220.45	$220.50
Purchase #7	$87.89	13.313%	$99.5908	$99.59	$99.60	$99.60
7 purchase totals =	$987.00		$1,073.6022	$1,073.59	$1,073.65	$1,073.60