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	$71.49	13.345%	$81.0303	$81.03	$81.05	$81.00
Purchase #2	$221.89	7.561%	$238.6671	$238.67	$238.65	$238.70
Purchase #3	$86.87	6.400%	$92.4297	$92.43	$92.45	$92.40
Purchase #4	$111.50	10.431%	$123.1306	$123.13	$123.15	$123.10
Purchase #5	$202.81	6.782%	$216.5646	$216.56	$216.55	$216.60
Purchase #6	$85.50	8.315%	$92.6093	$92.61	$92.60	$92.60
Purchase #7	$67.84	5.431%	$71.5244	$71.52	$71.50	$71.50
7 purchase totals =	$847.90		$915.9560	$915.95	$915.95	$915.90