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	$154.61	8.131%	$167.1813	$167.18	$167.20	$167.20
Purchase #2	$73.69	6.575%	$78.5351	$78.54	$78.55	$78.50
Purchase #3	$147.39	5.666%	$155.7411	$155.74	$155.75	$155.70
Purchase #4	$138.65	3.763%	$143.8674	$143.87	$143.85	$143.90
Purchase #5	$57.88	7.854%	$62.4259	$62.43	$62.45	$62.40
Purchase #6	$92.25	12.266%	$103.5654	$103.57	$103.55	$103.60
Purchase #7	$82.73	11.306%	$92.0835	$92.08	$92.10	$92.10
7 purchase totals =	$747.20		$803.3997	$803.41	$803.45	$803.40