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	$93.62	3.752%	$97.1326	$97.13	$97.15	$97.10
Purchase #2	$44.88	13.652%	$51.007	$51.01	$51.00	$51.00
Purchase #3	$49.33	9.795%	$54.1619	$54.16	$54.15	$54.20
Purchase #4	$18.44	12.344%	$20.7162	$20.72	$20.70	$20.70
Purchase #5	$128.53	6.655%	$137.0837	$137.08	$137.10	$137.10
Purchase #6	$166.79	5.460%	$175.8967	$175.90	$175.90	$175.90
Purchase #7	$90.99	13.759%	$103.5093	$103.51	$103.50	$103.50
7 purchase totals =	$592.58		$639.5074	$639.51	$639.50	$639.50