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	$241.62	3.461%	$249.9825	$249.98	$250.00	$250.00
Purchase #2	$54.36	4.616%	$56.8693	$56.87	$56.85	$56.90
Purchase #3	$21.66	3.740%	$22.4701	$22.47	$22.45	$22.50
Purchase #4	$59.67	9.491%	$65.3333	$65.33	$65.35	$65.30
Purchase #5	$72.77	9.750%	$79.8651	$79.87	$79.85	$79.90
Purchase #6	$88.80	12.413%	$99.8227	$99.82	$99.80	$99.80
Purchase #7	$99.88	4.538%	$104.4126	$104.41	$104.40	$104.40
7 purchase totals =	$638.76		$678.7556	$678.75	$678.70	$678.80