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	$50.77	11.430%	$56.573	$56.57	$56.55	$56.60
Purchase #2	$80.72	12.163%	$90.538	$90.54	$90.55	$90.50
Purchase #3	$41.47	11.556%	$46.2623	$46.26	$46.25	$46.30
Purchase #4	$83.33	8.234%	$90.1914	$90.19	$90.20	$90.20
Purchase #5	$237.36	5.362%	$250.0872	$250.09	$250.10	$250.10
Purchase #6	$108.58	13.132%	$122.8387	$122.84	$122.85	$122.80
Purchase #7	$200.69	10.502%	$221.7665	$221.77	$221.75	$221.80
7 purchase totals =	$802.92		$878.2571	$878.26	$878.25	$878.30