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	$250.81	6.464%	$267.0224	$267.02	$267.00	$267.00
Purchase #2	$74.50	5.781%	$78.8068	$78.81	$78.80	$78.80
Purchase #3	$200.67	8.450%	$217.6266	$217.63	$217.65	$217.60
Purchase #4	$90.58	12.174%	$101.6072	$101.61	$101.60	$101.60
Purchase #5	$115.91	13.767%	$131.8673	$131.87	$131.85	$131.90
Purchase #6	$25.59	13.561%	$29.0603	$29.06	$29.05	$29.10
Purchase #7	$147.46	5.417%	$155.4479	$155.45	$155.45	$155.40
7 purchase totals =	$905.52		$981.4385	$981.45	$981.40	$981.40