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	$128.26	10.188%	$141.3271	$141.33	$141.35	$141.30
Purchase #2	$233.38	6.795%	$249.2382	$249.24	$249.25	$249.20
Purchase #3	$59.48	4.594%	$62.2125	$62.21	$62.20	$62.20
Purchase #4	$55.95	7.147%	$59.9487	$59.95	$59.95	$59.90
Purchase #5	$31.28	9.616%	$34.2879	$34.29	$34.30	$34.30
Purchase #6	$143.75	10.138%	$158.3234	$158.32	$158.30	$158.30
Purchase #7	$71.74	5.254%	$75.5092	$75.51	$75.50	$75.50
7 purchase totals =	$723.84		$780.8470	$780.85	$780.85	$780.70