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	$245.79	13.517%	$279.0134	$279.01	$279.00	$279.00
Purchase #2	$58.84	11.386%	$65.5395	$65.54	$65.55	$65.50
Purchase #3	$53.84	10.567%	$59.5293	$59.53	$59.55	$59.50
Purchase #4	$111.65	12.455%	$125.556	$125.56	$125.55	$125.60
Purchase #5	$223.44	7.864%	$241.0113	$241.01	$241.00	$241.00
Purchase #6	$7.34	3.213%	$7.5758	$7.58	$7.60	$7.60
Purchase #7	$242.50	11.462%	$270.2954	$270.30	$270.30	$270.30
7 purchase totals =	$943.40		$1,048.5207	$1,048.53	$1,048.55	$1,048.50