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	$226.95	6.681%	$242.1125	$242.11	$242.10	$242.10
Purchase #2	$103.68	12.327%	$116.4606	$116.46	$116.45	$116.50
Purchase #3	$71.67	9.391%	$78.4005	$78.40	$78.40	$78.40
Purchase #4	$29.25	13.274%	$33.1326	$33.13	$33.15	$33.10
Purchase #5	$57.40	8.453%	$62.252	$62.25	$62.25	$62.30
Purchase #6	$136.84	3.369%	$141.4501	$141.45	$141.45	$141.50
Purchase #7	$30.80	3.380%	$31.841	$31.84	$31.85	$31.80
7 purchase totals =	$656.59		$705.6493	$705.64	$705.65	$705.70