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	$113.90	12.849%	$128.535	$128.54	$128.55	$128.50
Purchase #2	$178.42	4.149%	$185.8226	$185.82	$185.80	$185.80
Purchase #3	$183.65	10.669%	$203.2436	$203.24	$203.25	$203.20
Purchase #4	$136.45	7.130%	$146.1789	$146.18	$146.20	$146.20
Purchase #5	$201.44	8.399%	$218.3589	$218.36	$218.35	$218.40
Purchase #6	$177.32	5.735%	$187.4893	$187.49	$187.50	$187.50
Purchase #7	$130.47	7.218%	$139.8873	$139.89	$139.90	$139.90
7 purchase totals =	$1,121.65		$1,209.5156	$1,209.52	$1,209.55	$1,209.50