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	$111.84	7.564%	$120.2996	$120.30	$120.30	$120.30
Purchase #2	$79.76	3.857%	$82.8363	$82.84	$82.85	$82.80
Purchase #3	$136.79	8.404%	$148.2858	$148.29	$148.30	$148.30
Purchase #4	$36.91	12.248%	$41.4307	$41.43	$41.45	$41.40
Purchase #5	$11.44	9.113%	$12.4825	$12.48	$12.50	$12.50
Purchase #6	$189.68	5.764%	$200.6132	$200.61	$200.60	$200.60
Purchase #7	$172.27	7.153%	$184.5925	$184.59	$184.60	$184.60
7 purchase totals =	$738.69		$790.5406	$790.54	$790.60	$790.50