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	$57.72	6.799%	$61.6444	$61.64	$61.65	$61.60
Purchase #2	$33.89	3.785%	$35.1727	$35.17	$35.15	$35.20
Purchase #3	$219.59	13.597%	$249.4477	$249.45	$249.45	$249.40
Purchase #4	$141.41	4.408%	$147.6434	$147.64	$147.65	$147.60
Purchase #5	$45.46	6.730%	$48.5195	$48.52	$48.50	$48.50
Purchase #6	$158.32	10.558%	$175.0354	$175.04	$175.05	$175.00
Purchase #7	$54.27	9.368%	$59.354	$59.35	$59.35	$59.40
7 purchase totals =	$710.66		$776.8171	$776.81	$776.80	$776.70