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	$44.88	9.814%	$49.2845	$49.28	$49.30	$49.30
Purchase #2	$167.55	12.825%	$189.0383	$189.04	$189.05	$189.00
Purchase #3	$70.44	11.425%	$78.4878	$78.49	$78.50	$78.50
Purchase #4	$116.84	9.363%	$127.7797	$127.78	$127.80	$127.80
Purchase #5	$57.93	13.534%	$65.7702	$65.77	$65.75	$65.80
Purchase #6	$119.39	7.215%	$128.004	$128.00	$128.00	$128.00
Purchase #7	$250.83	6.868%	$268.057	$268.06	$268.05	$268.10
7 purchase totals =	$827.86		$906.4215	$906.42	$906.45	$906.50