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	$51.36	13.530%	$58.309	$58.31	$58.30	$58.30
Purchase #2	$129.31	7.715%	$139.2863	$139.29	$139.30	$139.30
Purchase #3	$155.88	5.406%	$164.3069	$164.31	$164.30	$164.30
Purchase #4	$88.86	3.124%	$91.636	$91.64	$91.65	$91.60
Purchase #5	$122.63	11.268%	$136.4479	$136.45	$136.45	$136.40
Purchase #6	$38.77	9.413%	$42.4194	$42.42	$42.40	$42.40
Purchase #7	$10.63	9.311%	$11.6198	$11.62	$11.60	$11.60
7 purchase totals =	$597.44		$644.0253	$644.04	$644.00	$643.90