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	$222.63	12.776%	$251.0732	$251.07	$251.05	$251.10
Purchase #2	$151.93	12.263%	$170.5612	$170.56	$170.55	$170.60
Purchase #3	$86.45	4.648%	$90.4682	$90.47	$90.45	$90.50
Purchase #4	$140.64	5.374%	$148.198	$148.20	$148.20	$148.20
Purchase #5	$38.58	13.639%	$43.8419	$43.84	$43.85	$43.80
Purchase #6	$48.92	13.344%	$55.4479	$55.45	$55.45	$55.40
Purchase #7	$78.50	3.477%	$81.2294	$81.23	$81.25	$81.20
7 purchase totals =	$767.65		$840.8198	$840.82	$840.80	$840.80