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	$120.41	6.235%	$127.9176	$127.92	$127.90	$127.90
Purchase #2	$225.77	6.803%	$241.1291	$241.13	$241.15	$241.10
Purchase #3	$135.69	11.769%	$151.6594	$151.66	$151.65	$151.70
Purchase #4	$227.86	12.529%	$256.4086	$256.41	$256.40	$256.40
Purchase #5	$147.40	4.377%	$153.8517	$153.85	$153.85	$153.90
Purchase #6	$121.39	6.559%	$129.352	$129.35	$129.35	$129.40
Purchase #7	$137.45	12.689%	$154.891	$154.89	$154.90	$154.90
7 purchase totals =	$1,115.97		$1,215.2094	$1,215.21	$1,215.20	$1,215.30