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	$231.86	6.652%	$247.2833	$247.28	$247.30	$247.30
Purchase #2	$111.45	10.675%	$123.3473	$123.35	$123.35	$123.30
Purchase #3	$193.25	10.470%	$213.4833	$213.48	$213.50	$213.50
Purchase #4	$115.90	6.665%	$123.6247	$123.62	$123.60	$123.60
Purchase #5	$136.25	11.379%	$151.7539	$151.75	$151.75	$151.80
Purchase #6	$82.25	12.498%	$92.5296	$92.53	$92.55	$92.50
Purchase #7	$123.87	4.710%	$129.7043	$129.70	$129.70	$129.70
7 purchase totals =	$994.83		$1,081.7264	$1,081.71	$1,081.75	$1,081.70