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	$166.98	8.309%	$180.8544	$180.85	$180.85	$180.90
Purchase #2	$33.89	11.538%	$37.8002	$37.80	$37.80	$37.80
Purchase #3	$110.92	4.608%	$116.0312	$116.03	$116.05	$116.00
Purchase #4	$136.47	5.818%	$144.4098	$144.41	$144.40	$144.40
Purchase #5	$191.60	12.767%	$216.0616	$216.06	$216.05	$216.10
Purchase #6	$151.69	7.371%	$162.8711	$162.87	$162.85	$162.90
Purchase #7	$97.98	4.705%	$102.59	$102.59	$102.60	$102.60
7 purchase totals =	$889.53		$960.6183	$960.61	$960.60	$960.70