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	$118.30	10.383%	$130.5831	$130.58	$130.60	$130.60
Purchase #2	$241.36	3.802%	$250.5365	$250.54	$250.55	$250.50
Purchase #3	$80.72	10.457%	$89.1609	$89.16	$89.15	$89.20
Purchase #4	$84.76	4.377%	$88.4699	$88.47	$88.45	$88.50
Purchase #5	$36.31	8.151%	$39.2696	$39.27	$39.25	$39.30
Purchase #6	$101.46	5.448%	$106.9875	$106.99	$107.00	$107.00
Purchase #7	$150.77	12.285%	$169.2921	$169.29	$169.30	$169.30
7 purchase totals =	$813.68		$874.2996	$874.30	$874.30	$874.40