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	$143.54	9.162%	$156.6911	$156.69	$156.70	$156.70
Purchase #2	$115.61	6.524%	$123.1524	$123.15	$123.15	$123.20
Purchase #3	$55.65	6.113%	$59.0519	$59.05	$59.05	$59.10
Purchase #4	$127.79	8.697%	$138.9039	$138.90	$138.90	$138.90
Purchase #5	$49.98	11.656%	$55.8057	$55.81	$55.80	$55.80
Purchase #6	$15.70	6.781%	$16.7646	$16.76	$16.75	$16.80
Purchase #7	$40.83	5.447%	$43.054	$43.05	$43.05	$43.10
7 purchase totals =	$549.10		$593.4236	$593.41	$593.40	$593.60