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	$81.67	9.779%	$89.6565	$89.66	$89.65	$89.70
Purchase #2	$157.26	5.109%	$165.2944	$165.29	$165.30	$165.30
Purchase #3	$5.48	9.305%	$5.9899	$5.99	$6.00	$6.00
Purchase #4	$18.44	10.269%	$20.3336	$20.33	$20.35	$20.30
Purchase #5	$90.94	9.272%	$99.372	$99.37	$99.35	$99.40
Purchase #6	$125.67	6.477%	$133.8096	$133.81	$133.80	$133.80
Purchase #7	$51.89	13.698%	$58.9979	$59.00	$59.00	$59.00
7 purchase totals =	$531.35		$573.4539	$573.45	$573.45	$573.50