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	$68.71	11.487%	$76.6027	$76.60	$76.60	$76.60
Purchase #2	$80.58	10.843%	$89.3173	$89.32	$89.30	$89.30
Purchase #3	$62.40	11.240%	$69.4138	$69.41	$69.40	$69.40
Purchase #4	$119.52	7.799%	$128.8414	$128.84	$128.85	$128.80
Purchase #5	$160.87	7.259%	$172.5476	$172.55	$172.55	$172.50
Purchase #6	$88.99	13.118%	$100.6637	$100.66	$100.65	$100.70
Purchase #7	$200.87	4.278%	$209.4632	$209.46	$209.45	$209.50
7 purchase totals =	$781.94		$846.8497	$846.84	$846.80	$846.80