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	$234.43	6.352%	$249.321	$249.32	$249.30	$249.30
Purchase #2	$97.72	3.245%	$100.891	$100.89	$100.90	$100.90
Purchase #3	$122.68	12.829%	$138.4186	$138.42	$138.40	$138.40
Purchase #4	$169.95	10.707%	$188.1465	$188.15	$188.15	$188.10
Purchase #5	$104.73	3.240%	$108.1233	$108.12	$108.10	$108.10
Purchase #6	$211.73	10.285%	$233.5064	$233.51	$233.50	$233.50
Purchase #7	$65.78	11.474%	$73.3276	$73.33	$73.35	$73.30
7 purchase totals =	$1,007.02		$1,091.7344	$1,091.74	$1,091.70	$1,091.60