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	$127.72	5.821%	$135.1546	$135.15	$135.15	$135.20
Purchase #2	$99.99	11.624%	$111.6128	$111.61	$111.60	$111.60
Purchase #3	$48.26	4.600%	$50.48	$50.48	$50.50	$50.50
Purchase #4	$238.40	4.708%	$249.6239	$249.62	$249.60	$249.60
Purchase #5	$18.95	5.660%	$20.0226	$20.02	$20.00	$20.00
Purchase #6	$19.27	9.507%	$21.102	$21.10	$21.10	$21.10
Purchase #7	$83.26	12.250%	$93.4594	$93.46	$93.45	$93.50
7 purchase totals =	$635.85		$681.4553	$681.44	$681.40	$681.50