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	$127.48	13.321%	$144.4616	$144.46	$144.45	$144.50
Purchase #2	$67.98	12.419%	$76.4224	$76.42	$76.40	$76.40
Purchase #3	$86.87	4.453%	$90.7383	$90.74	$90.75	$90.70
Purchase #4	$35.70	10.441%	$39.4274	$39.43	$39.45	$39.40
Purchase #5	$72.85	9.788%	$79.9806	$79.98	$80.00	$80.00
Purchase #6	$226.83	5.815%	$240.0202	$240.02	$240.00	$240.00
Purchase #7	$39.95	5.319%	$42.0749	$42.07	$42.05	$42.10
7 purchase totals =	$657.66		$713.1254	$713.12	$713.10	$713.10