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	$83.66	7.210%	$89.6919	$89.69	$89.70	$89.70
Purchase #2	$117.64	10.832%	$130.3828	$130.38	$130.40	$130.40
Purchase #3	$64.58	13.519%	$73.3106	$73.31	$73.30	$73.30
Purchase #4	$248.66	8.501%	$269.7986	$269.80	$269.80	$269.80
Purchase #5	$250.60	11.862%	$280.3262	$280.33	$280.35	$280.30
Purchase #6	$206.76	7.144%	$221.5309	$221.53	$221.55	$221.50
Purchase #7	$69.85	11.327%	$77.7619	$77.76	$77.75	$77.80
7 purchase totals =	$1,041.75		$1,142.8029	$1,142.80	$1,142.85	$1,142.80