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	$233.94	13.118%	$264.6282	$264.63	$264.65	$264.60
Purchase #2	$187.70	3.590%	$194.4384	$194.44	$194.45	$194.40
Purchase #3	$98.34	11.241%	$109.3944	$109.39	$109.40	$109.40
Purchase #4	$115.57	13.683%	$131.3834	$131.38	$131.40	$131.40
Purchase #5	$38.28	11.848%	$42.8154	$42.82	$42.80	$42.80
Purchase #6	$34.96	6.828%	$37.3471	$37.35	$37.35	$37.30
Purchase #7	$118.39	9.431%	$129.5554	$129.56	$129.55	$129.60
7 purchase totals =	$827.18		$909.5623	$909.57	$909.60	$909.50