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	$134.64	12.295%	$151.194	$151.19	$151.20	$151.20
Purchase #2	$248.36	10.164%	$273.6033	$273.60	$273.60	$273.60
Purchase #3	$127.79	7.321%	$137.1455	$137.15	$137.15	$137.10
Purchase #4	$248.75	10.569%	$275.0404	$275.04	$275.05	$275.00
Purchase #5	$131.25	12.717%	$147.9411	$147.94	$147.95	$147.90
Purchase #6	$99.98	11.331%	$111.3087	$111.31	$111.30	$111.30
Purchase #7	$164.65	13.165%	$186.3262	$186.33	$186.35	$186.30
7 purchase totals =	$1,155.42		$1,282.5592	$1,282.56	$1,282.60	$1,282.40