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	$164.86	13.567%	$187.2266	$187.23	$187.25	$187.20
Purchase #2	$196.92	12.647%	$221.8245	$221.82	$221.80	$221.80
Purchase #3	$44.82	7.134%	$48.0175	$48.02	$48.00	$48.00
Purchase #4	$140.93	8.440%	$152.8245	$152.82	$152.80	$152.80
Purchase #5	$115.35	4.659%	$120.7242	$120.72	$120.70	$120.70
Purchase #6	$53.67	11.417%	$59.7975	$59.80	$59.80	$59.80
Purchase #7	$51.39	3.539%	$53.2087	$53.21	$53.20	$53.20
7 purchase totals =	$767.94		$843.6235	$843.62	$843.55	$843.50