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	$125.55	9.431%	$137.3906	$137.39	$137.40	$137.40
Purchase #2	$50.49	8.359%	$54.7105	$54.71	$54.70	$54.70
Purchase #3	$86.90	11.828%	$97.1785	$97.18	$97.20	$97.20
Purchase #4	$151.66	13.368%	$171.9339	$171.93	$171.95	$171.90
Purchase #5	$225.64	12.421%	$253.6667	$253.67	$253.65	$253.70
Purchase #6	$54.53	4.281%	$56.8644	$56.86	$56.85	$56.90
Purchase #7	$121.71	4.689%	$127.417	$127.42	$127.40	$127.40
7 purchase totals =	$816.48		$899.1616	$899.16	$899.15	$899.20