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	$69.83	7.787%	$75.2677	$75.27	$75.25	$75.30
Purchase #2	$78.35	13.703%	$89.0863	$89.09	$89.10	$89.10
Purchase #3	$98.69	5.533%	$104.1505	$104.15	$104.15	$104.20
Purchase #4	$77.64	10.462%	$85.7627	$85.76	$85.75	$85.80
Purchase #5	$172.38	3.579%	$178.5495	$178.55	$178.55	$178.50
Purchase #6	$80.65	10.573%	$89.1771	$89.18	$89.20	$89.20
Purchase #7	$210.66	6.283%	$223.8958	$223.90	$223.90	$223.90
7 purchase totals =	$788.20		$845.8896	$845.90	$845.90	$846.00