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	$248.50	8.168%	$268.7975	$268.80	$268.80	$268.80
Purchase #2	$141.64	10.530%	$156.5547	$156.55	$156.55	$156.60
Purchase #3	$26.96	10.233%	$29.7188	$29.72	$29.70	$29.70
Purchase #4	$98.29	7.118%	$105.2863	$105.29	$105.30	$105.30
Purchase #5	$124.26	3.434%	$128.5271	$128.53	$128.55	$128.50
Purchase #6	$207.74	12.530%	$233.7698	$233.77	$233.75	$233.80
Purchase #7	$91.90	9.396%	$100.5349	$100.53	$100.55	$100.50
7 purchase totals =	$939.29		$1,023.1891	$1,023.19	$1,023.20	$1,023.20