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	$123.28	12.517%	$138.711	$138.71	$138.70	$138.70
Purchase #2	$72.98	11.355%	$81.2669	$81.27	$81.25	$81.30
Purchase #3	$185.72	11.788%	$207.6127	$207.61	$207.60	$207.60
Purchase #4	$165.50	3.841%	$171.8569	$171.86	$171.85	$171.90
Purchase #5	$113.63	13.153%	$128.5758	$128.58	$128.60	$128.60
Purchase #6	$223.83	8.668%	$243.2316	$243.23	$243.25	$243.20
Purchase #7	$108.94	4.873%	$114.2486	$114.25	$114.25	$114.20
7 purchase totals =	$993.88		$1,085.5035	$1,085.51	$1,085.50	$1,085.50