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	$245.64	13.809%	$279.5604	$279.56	$279.55	$279.60
Purchase #2	$40.95	10.710%	$45.3357	$45.34	$45.35	$45.30
Purchase #3	$63.71	4.552%	$66.6101	$66.61	$66.60	$66.60
Purchase #4	$80.94	8.525%	$87.8401	$87.84	$87.85	$87.80
Purchase #5	$125.90	12.728%	$141.9246	$141.92	$141.90	$141.90
Purchase #6	$56.77	5.510%	$59.898	$59.90	$59.90	$59.90
Purchase #7	$223.95	8.253%	$242.4326	$242.43	$242.45	$242.40
7 purchase totals =	$837.86		$923.6015	$923.60	$923.60	$923.50