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	$134.79	5.599%	$142.3369	$142.34	$142.35	$142.30
Purchase #2	$56.25	9.534%	$61.6129	$61.61	$61.60	$61.60
Purchase #3	$58.80	6.249%	$62.4744	$62.47	$62.45	$62.50
Purchase #4	$102.28	12.553%	$115.1192	$115.12	$115.10	$115.10
Purchase #5	$30.57	9.670%	$33.5261	$33.53	$33.55	$33.50
Purchase #6	$10.77	13.504%	$12.2244	$12.22	$12.20	$12.20
Purchase #7	$109.35	4.108%	$113.8421	$113.84	$113.85	$113.80
7 purchase totals =	$502.81		$541.1360	$541.13	$541.10	$541.00