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	$103.85	5.605%	$109.6708	$109.67	$109.65	$109.70
Purchase #2	$229.46	7.688%	$247.1009	$247.10	$247.10	$247.10
Purchase #3	$33.67	11.677%	$37.6016	$37.60	$37.60	$37.60
Purchase #4	$116.45	6.374%	$123.8725	$123.87	$123.85	$123.90
Purchase #5	$84.65	4.589%	$88.5346	$88.53	$88.55	$88.50
Purchase #6	$168.67	12.310%	$189.4333	$189.43	$189.45	$189.40
Purchase #7	$68.84	9.701%	$75.5182	$75.52	$75.50	$75.50
7 purchase totals =	$805.59		$871.7319	$871.72	$871.70	$871.70