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	$142.77	5.823%	$151.0835	$151.08	$151.10	$151.10
Purchase #2	$60.35	12.588%	$67.9469	$67.95	$67.95	$67.90
Purchase #3	$93.33	7.670%	$100.4884	$100.49	$100.50	$100.50
Purchase #4	$148.54	10.719%	$164.462	$164.46	$164.45	$164.50
Purchase #5	$153.69	9.332%	$168.0324	$168.03	$168.05	$168.00
Purchase #6	$91.30	10.408%	$100.8025	$100.80	$100.80	$100.80
Purchase #7	$42.48	6.698%	$45.3253	$45.33	$45.35	$45.30
7 purchase totals =	$732.46		$798.1410	$798.14	$798.20	$798.10