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	$135.70	10.378%	$149.7829	$149.78	$149.80	$149.80
Purchase #2	$215.77	6.342%	$229.4541	$229.45	$229.45	$229.50
Purchase #3	$76.48	11.327%	$85.1429	$85.14	$85.15	$85.10
Purchase #4	$192.55	4.293%	$200.8162	$200.82	$200.80	$200.80
Purchase #5	$64.31	12.677%	$72.4626	$72.46	$72.45	$72.50
Purchase #6	$78.65	4.698%	$82.345	$82.35	$82.35	$82.30
Purchase #7	$242.52	6.706%	$258.7834	$258.78	$258.80	$258.80
7 purchase totals =	$1,005.98		$1,078.7871	$1,078.78	$1,078.80	$1,078.80