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	$159.38	3.829%	$165.4827	$165.48	$165.50	$165.50
Purchase #2	$46.69	12.414%	$52.4861	$52.49	$52.50	$52.50
Purchase #3	$148.69	13.120%	$168.1981	$168.20	$168.20	$168.20
Purchase #4	$7.64	3.262%	$7.8892	$7.89	$7.90	$7.90
Purchase #5	$27.74	7.252%	$29.7517	$29.75	$29.75	$29.80
Purchase #6	$214.33	4.303%	$223.5526	$223.55	$223.55	$223.60
Purchase #7	$234.60	9.623%	$257.1756	$257.18	$257.20	$257.20
7 purchase totals =	$839.07		$904.5360	$904.54	$904.60	$904.70