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	$248.97	9.784%	$273.3292	$273.33	$273.35	$273.30
Purchase #2	$127.96	10.347%	$141.2	$141.20	$141.20	$141.20
Purchase #3	$117.95	7.536%	$126.8387	$126.84	$126.85	$126.80
Purchase #4	$147.70	12.576%	$166.2748	$166.27	$166.25	$166.30
Purchase #5	$130.69	5.496%	$137.8727	$137.87	$137.85	$137.90
Purchase #6	$118.43	9.872%	$130.1214	$130.12	$130.10	$130.10
Purchase #7	$118.63	12.859%	$133.8846	$133.88	$133.90	$133.90
7 purchase totals =	$1,010.33		$1,109.5214	$1,109.51	$1,109.50	$1,109.50