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	$85.57	5.657%	$90.4107	$90.41	$90.40	$90.40
Purchase #2	$229.31	8.305%	$248.3542	$248.35	$248.35	$248.40
Purchase #3	$212.42	7.826%	$229.044	$229.04	$229.05	$229.00
Purchase #4	$169.74	9.418%	$185.7261	$185.73	$185.75	$185.70
Purchase #5	$133.33	9.839%	$146.4483	$146.45	$146.45	$146.40
Purchase #6	$49.52	4.131%	$51.5657	$51.57	$51.55	$51.60
Purchase #7	$204.37	12.343%	$229.5954	$229.60	$229.60	$229.60
7 purchase totals =	$1,084.26		$1,181.1444	$1,181.15	$1,181.15	$1,181.10