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	$74.84	5.423%	$78.8986	$78.90	$78.90	$78.90
Purchase #2	$90.53	10.516%	$100.0501	$100.05	$100.05	$100.10
Purchase #3	$37.57	13.700%	$42.7171	$42.72	$42.70	$42.70
Purchase #4	$71.29	13.397%	$80.8407	$80.84	$80.85	$80.80
Purchase #5	$228.80	11.571%	$255.2744	$255.27	$255.25	$255.30
Purchase #6	$152.82	12.646%	$172.1456	$172.15	$172.15	$172.10
Purchase #7	$79.76	5.489%	$84.138	$84.14	$84.15	$84.10
7 purchase totals =	$735.61		$814.0645	$814.07	$814.05	$814.00