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	$18.96	3.670%	$19.6558	$19.66	$19.65	$19.70
Purchase #2	$183.32	9.559%	$200.8436	$200.84	$200.85	$200.80
Purchase #3	$187.40	5.744%	$198.1643	$198.16	$198.15	$198.20
Purchase #4	$102.73	9.385%	$112.3712	$112.37	$112.35	$112.40
Purchase #5	$207.89	5.785%	$219.9164	$219.92	$219.90	$219.90
Purchase #6	$100.74	4.291%	$105.0628	$105.06	$105.05	$105.10
Purchase #7	$52.76	12.708%	$59.4647	$59.46	$59.45	$59.50
7 purchase totals =	$853.80		$915.4788	$915.47	$915.40	$915.60