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	$74.29	5.857%	$78.6412	$78.64	$78.65	$78.60
Purchase #2	$198.25	8.766%	$215.6286	$215.63	$215.65	$215.60
Purchase #3	$52.88	4.835%	$55.4367	$55.44	$55.45	$55.40
Purchase #4	$91.72	6.188%	$97.3956	$97.40	$97.40	$97.40
Purchase #5	$5.68	8.639%	$6.1707	$6.17	$6.15	$6.20
Purchase #6	$33.69	12.598%	$37.9343	$37.93	$37.95	$37.90
Purchase #7	$206.25	4.424%	$215.3745	$215.37	$215.35	$215.40
7 purchase totals =	$662.76		$706.5816	$706.58	$706.60	$706.50