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	$59.94	11.533%	$66.8529	$66.85	$66.85	$66.90
Purchase #2	$86.96	10.685%	$96.2517	$96.25	$96.25	$96.30
Purchase #3	$175.69	5.194%	$184.8153	$184.82	$184.80	$184.80
Purchase #4	$85.27	12.272%	$95.7343	$95.73	$95.75	$95.70
Purchase #5	$232.70	3.832%	$241.6171	$241.62	$241.60	$241.60
Purchase #6	$183.85	9.218%	$200.7973	$200.80	$200.80	$200.80
Purchase #7	$165.76	3.518%	$171.5914	$171.59	$171.60	$171.60
7 purchase totals =	$990.17		$1,057.6600	$1,057.66	$1,057.65	$1,057.70