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	$83.87	7.345%	$90.0303	$90.03	$90.05	$90.00
Purchase #2	$155.31	4.245%	$161.9029	$161.90	$161.90	$161.90
Purchase #3	$89.42	6.482%	$95.2162	$95.22	$95.20	$95.20
Purchase #4	$107.59	10.293%	$118.6642	$118.66	$118.65	$118.70
Purchase #5	$69.37	4.443%	$72.4521	$72.45	$72.45	$72.50
Purchase #6	$125.45	6.743%	$133.9091	$133.91	$133.90	$133.90
Purchase #7	$110.91	7.822%	$119.5854	$119.59	$119.60	$119.60
7 purchase totals =	$741.92		$791.7602	$791.76	$791.75	$791.80