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	$163.54	4.730%	$171.2754	$171.28	$171.30	$171.30
Purchase #2	$159.89	13.763%	$181.8957	$181.90	$181.90	$181.90
Purchase #3	$65.48	12.752%	$73.83	$73.83	$73.85	$73.80
Purchase #4	$130.92	5.637%	$138.3	$138.30	$138.30	$138.30
Purchase #5	$136.74	3.406%	$141.3974	$141.40	$141.40	$141.40
Purchase #6	$16.45	11.791%	$18.3896	$18.39	$18.40	$18.40
Purchase #7	$179.57	13.341%	$203.5264	$203.53	$203.55	$203.50
7 purchase totals =	$852.59		$928.6145	$928.63	$928.70	$928.60