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	$53.40	9.622%	$58.5381	$58.54	$58.55	$58.50
Purchase #2	$225.71	11.105%	$250.7751	$250.78	$250.80	$250.80
Purchase #3	$58.83	11.511%	$65.6019	$65.60	$65.60	$65.60
Purchase #4	$108.37	13.712%	$123.2297	$123.23	$123.25	$123.20
Purchase #5	$6.50	5.129%	$6.8334	$6.83	$6.85	$6.80
Purchase #6	$133.56	13.398%	$151.4544	$151.45	$151.45	$151.50
Purchase #7	$180.94	4.695%	$189.4351	$189.44	$189.45	$189.40
7 purchase totals =	$767.31		$845.8677	$845.87	$845.95	$845.80