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	$95.78	8.811%	$104.2192	$104.22	$104.20	$104.20
Purchase #2	$56.66	4.740%	$59.3457	$59.35	$59.35	$59.30
Purchase #3	$77.52	10.332%	$85.5294	$85.53	$85.55	$85.50
Purchase #4	$148.92	5.272%	$156.7711	$156.77	$156.75	$156.80
Purchase #5	$241.33	12.619%	$271.7834	$271.78	$271.80	$271.80
Purchase #6	$249.53	13.559%	$283.3638	$283.36	$283.35	$283.40
Purchase #7	$38.38	7.206%	$41.1457	$41.15	$41.15	$41.10
7 purchase totals =	$908.12		$1,002.1583	$1,002.16	$1,002.15	$1,002.10