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	$145.27	3.366%	$150.1598	$150.16	$150.15	$150.20
Purchase #2	$91.79	8.342%	$99.4471	$99.45	$99.45	$99.40
Purchase #3	$191.44	3.593%	$198.3184	$198.32	$198.30	$198.30
Purchase #4	$52.99	7.318%	$56.8678	$56.87	$56.85	$56.90
Purchase #5	$72.94	10.316%	$80.4645	$80.46	$80.45	$80.50
Purchase #6	$117.41	5.747%	$124.1576	$124.16	$124.15	$124.20
Purchase #7	$140.93	3.834%	$146.3333	$146.33	$146.35	$146.30
7 purchase totals =	$812.77		$855.7485	$855.75	$855.70	$855.80