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	$71.31	11.510%	$79.5178	$79.52	$79.50	$79.50
Purchase #2	$179.32	3.409%	$185.433	$185.43	$185.45	$185.40
Purchase #3	$59.65	8.745%	$64.8664	$64.87	$64.85	$64.90
Purchase #4	$35.67	5.319%	$37.5673	$37.57	$37.55	$37.60
Purchase #5	$5.77	9.477%	$6.3168	$6.32	$6.30	$6.30
Purchase #6	$207.50	7.131%	$222.2968	$222.30	$222.30	$222.30
Purchase #7	$105.76	7.122%	$113.2922	$113.29	$113.30	$113.30
7 purchase totals =	$664.98		$709.2903	$709.30	$709.25	$709.30