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	$31.98	6.874%	$34.1783	$34.18	$34.20	$34.20
Purchase #2	$171.86	4.170%	$179.0266	$179.03	$179.05	$179.00
Purchase #3	$229.73	10.455%	$253.7483	$253.75	$253.75	$253.70
Purchase #4	$109.88	13.119%	$124.2952	$124.30	$124.30	$124.30
Purchase #5	$183.28	4.478%	$191.4873	$191.49	$191.50	$191.50
Purchase #6	$138.47	4.228%	$144.3245	$144.32	$144.30	$144.30
Purchase #7	$233.52	5.123%	$245.4832	$245.48	$245.50	$245.50
7 purchase totals =	$1,098.72		$1,172.5434	$1,172.55	$1,172.60	$1,172.50