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	$236.73	11.650%	$264.309	$264.31	$264.30	$264.30
Purchase #2	$127.82	7.579%	$137.5075	$137.51	$137.50	$137.50
Purchase #3	$145.45	8.763%	$158.1958	$158.20	$158.20	$158.20
Purchase #4	$174.43	12.562%	$196.3419	$196.34	$196.35	$196.30
Purchase #5	$159.92	3.844%	$166.0673	$166.07	$166.05	$166.10
Purchase #6	$83.63	3.643%	$86.6766	$86.68	$86.70	$86.70
Purchase #7	$132.77	10.868%	$147.1994	$147.20	$147.20	$147.20
7 purchase totals =	$1,060.75		$1,156.2975	$1,156.31	$1,156.30	$1,156.30