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	$152.47	12.199%	$171.0698	$171.07	$171.05	$171.10
Purchase #2	$216.68	7.571%	$233.0848	$233.08	$233.10	$233.10
Purchase #3	$144.37	5.629%	$152.4966	$152.50	$152.50	$152.50
Purchase #4	$94.85	13.324%	$107.4878	$107.49	$107.50	$107.50
Purchase #5	$17.28	4.737%	$18.0986	$18.10	$18.10	$18.10
Purchase #6	$127.40	10.499%	$140.7757	$140.78	$140.80	$140.80
Purchase #7	$102.96	5.218%	$108.3325	$108.33	$108.35	$108.30
7 purchase totals =	$856.01		$931.3458	$931.35	$931.40	$931.40