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	$7.79	3.429%	$8.0571	$8.06	$8.05	$8.10
Purchase #2	$19.64	4.498%	$20.5234	$20.52	$20.50	$20.50
Purchase #3	$136.40	9.853%	$149.8395	$149.84	$149.85	$149.80
Purchase #4	$73.98	5.621%	$78.1384	$78.14	$78.15	$78.10
Purchase #5	$168.66	3.467%	$174.5074	$174.51	$174.50	$174.50
Purchase #6	$18.71	10.331%	$20.6429	$20.64	$20.65	$20.60
Purchase #7	$64.40	12.186%	$72.2478	$72.25	$72.25	$72.20
7 purchase totals =	$489.58		$523.9565	$523.96	$523.95	$523.80