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	$73.43	8.311%	$79.5328	$79.53	$79.55	$79.50
Purchase #2	$118.60	13.378%	$134.4663	$134.47	$134.45	$134.50
Purchase #3	$213.37	3.802%	$221.4823	$221.48	$221.50	$221.50
Purchase #4	$105.82	6.860%	$113.0793	$113.08	$113.10	$113.10
Purchase #5	$73.28	8.673%	$79.6356	$79.64	$79.65	$79.60
Purchase #6	$152.34	13.411%	$172.7703	$172.77	$172.75	$172.80
Purchase #7	$92.76	7.378%	$99.6038	$99.60	$99.60	$99.60
7 purchase totals =	$829.60		$900.5704	$900.57	$900.60	$900.60