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	$102.72	12.713%	$115.7788	$115.78	$115.80	$115.80
Purchase #2	$130.78	12.161%	$146.6842	$146.68	$146.70	$146.70
Purchase #3	$47.50	6.141%	$50.417	$50.42	$50.40	$50.40
Purchase #4	$57.49	12.712%	$64.7981	$64.80	$64.80	$64.80
Purchase #5	$74.38	10.505%	$82.1936	$82.19	$82.20	$82.20
Purchase #6	$53.70	5.226%	$56.5064	$56.51	$56.50	$56.50
Purchase #7	$244.78	10.501%	$270.4843	$270.48	$270.50	$270.50
7 purchase totals =	$711.35		$786.8624	$786.86	$786.90	$786.90