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	$201.79	10.584%	$223.1475	$223.15	$223.15	$223.10
Purchase #2	$235.57	7.837%	$254.0316	$254.03	$254.05	$254.00
Purchase #3	$138.72	4.753%	$145.3134	$145.31	$145.30	$145.30
Purchase #4	$86.48	3.410%	$89.429	$89.43	$89.45	$89.40
Purchase #5	$174.82	9.522%	$191.4664	$191.47	$191.45	$191.50
Purchase #6	$103.74	13.625%	$117.8746	$117.87	$117.85	$117.90
Purchase #7	$63.86	6.232%	$67.8398	$67.84	$67.85	$67.80
7 purchase totals =	$1,004.98		$1,089.1023	$1,089.10	$1,089.10	$1,089.00