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	$50.35	5.599%	$53.1691	$53.17	$53.15	$53.20
Purchase #2	$187.90	6.814%	$200.7035	$200.70	$200.70	$200.70
Purchase #3	$62.72	4.160%	$65.3292	$65.33	$65.35	$65.30
Purchase #4	$248.88	9.282%	$271.981	$271.98	$272.00	$272.00
Purchase #5	$212.65	5.274%	$223.8652	$223.87	$223.85	$223.90
Purchase #6	$72.75	13.397%	$82.4963	$82.50	$82.50	$82.50
Purchase #7	$115.45	6.650%	$123.1274	$123.13	$123.15	$123.10
7 purchase totals =	$950.70		$1,020.6717	$1,020.68	$1,020.70	$1,020.70