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	$144.36	3.831%	$149.8904	$149.89	$149.90	$149.90
Purchase #2	$72.96	5.657%	$77.0873	$77.09	$77.10	$77.10
Purchase #3	$242.92	5.553%	$256.4093	$256.41	$256.40	$256.40
Purchase #4	$57.50	8.297%	$62.2708	$62.27	$62.25	$62.30
Purchase #5	$96.27	4.242%	$100.3538	$100.35	$100.35	$100.40
Purchase #6	$36.69	4.349%	$38.2856	$38.29	$38.30	$38.30
Purchase #7	$129.32	8.441%	$140.2359	$140.24	$140.25	$140.20
7 purchase totals =	$780.02		$824.5331	$824.54	$824.55	$824.60