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	$159.85	5.422%	$168.5171	$168.52	$168.50	$168.50
Purchase #2	$39.81	7.796%	$42.9136	$42.91	$42.90	$42.90
Purchase #3	$146.63	4.177%	$152.7547	$152.75	$152.75	$152.80
Purchase #4	$5.82	9.182%	$6.3544	$6.35	$6.35	$6.40
Purchase #5	$180.28	6.714%	$192.384	$192.38	$192.40	$192.40
Purchase #6	$179.90	6.248%	$191.1402	$191.14	$191.15	$191.10
Purchase #7	$78.68	5.332%	$82.8752	$82.88	$82.90	$82.90
7 purchase totals =	$790.97		$836.9392	$836.93	$836.95	$837.00