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	$149.69	13.219%	$169.4775	$169.48	$169.50	$169.50
Purchase #2	$46.74	6.604%	$49.8267	$49.83	$49.85	$49.80
Purchase #3	$114.65	7.630%	$123.3978	$123.40	$123.40	$123.40
Purchase #4	$89.41	12.195%	$100.3135	$100.31	$100.30	$100.30
Purchase #5	$59.51	9.836%	$65.3634	$65.36	$65.35	$65.40
Purchase #6	$167.50	9.599%	$183.5783	$183.58	$183.60	$183.60
Purchase #7	$140.25	7.238%	$150.4013	$150.40	$150.40	$150.40
7 purchase totals =	$767.75		$842.3585	$842.36	$842.40	$842.40