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	$39.60	4.506%	$41.3844	$41.38	$41.40	$41.40
Purchase #2	$135.92	10.213%	$149.8015	$149.80	$149.80	$149.80
Purchase #3	$38.33	13.197%	$43.3884	$43.39	$43.40	$43.40
Purchase #4	$105.95	3.478%	$109.6349	$109.63	$109.65	$109.60
Purchase #5	$6.86	7.746%	$7.3914	$7.39	$7.40	$7.40
Purchase #6	$159.70	7.391%	$171.5034	$171.50	$171.50	$171.50
Purchase #7	$58.50	12.137%	$65.6001	$65.60	$65.60	$65.60
7 purchase totals =	$544.86		$588.7041	$588.69	$588.75	$588.70