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	$100.70	8.331%	$109.0893	$109.09	$109.10	$109.10
Purchase #2	$137.45	8.672%	$149.3697	$149.37	$149.35	$149.40
Purchase #3	$16.31	12.268%	$18.3109	$18.31	$18.30	$18.30
Purchase #4	$111.65	7.117%	$119.5961	$119.60	$119.60	$119.60
Purchase #5	$166.56	3.539%	$172.4546	$172.45	$172.45	$172.50
Purchase #6	$173.46	8.755%	$188.6464	$188.65	$188.65	$188.60
Purchase #7	$31.44	6.394%	$33.4503	$33.45	$33.45	$33.50
7 purchase totals =	$737.57		$790.9173	$790.92	$790.90	$791.00