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	$158.79	13.539%	$180.2886	$180.29	$180.30	$180.30
Purchase #2	$18.46	11.332%	$20.5519	$20.55	$20.55	$20.60
Purchase #3	$176.39	13.720%	$200.5907	$200.59	$200.60	$200.60
Purchase #4	$95.74	11.218%	$106.4801	$106.48	$106.50	$106.50
Purchase #5	$46.72	4.317%	$48.7369	$48.74	$48.75	$48.70
Purchase #6	$37.52	10.562%	$41.4829	$41.48	$41.50	$41.50
Purchase #7	$90.68	12.799%	$102.2861	$102.29	$102.30	$102.30
7 purchase totals =	$624.30		$700.4172	$700.42	$700.50	$700.50