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	$162.31	11.743%	$181.3701	$181.37	$181.35	$181.40
Purchase #2	$233.94	7.326%	$251.0784	$251.08	$251.10	$251.10
Purchase #3	$117.31	5.233%	$123.4488	$123.45	$123.45	$123.40
Purchase #4	$141.84	9.822%	$155.7715	$155.77	$155.75	$155.80
Purchase #5	$30.28	7.481%	$32.5452	$32.55	$32.55	$32.50
Purchase #6	$33.66	5.501%	$35.5116	$35.51	$35.50	$35.50
Purchase #7	$29.81	3.556%	$30.87	$30.87	$30.85	$30.90
7 purchase totals =	$749.15		$810.5956	$810.60	$810.55	$810.60