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	$50.75	13.139%	$57.418	$57.42	$57.40	$57.40
Purchase #2	$234.43	12.641%	$264.0643	$264.06	$264.05	$264.10
Purchase #3	$164.66	7.406%	$176.8547	$176.85	$176.85	$176.90
Purchase #4	$178.96	3.432%	$185.1019	$185.10	$185.10	$185.10
Purchase #5	$89.55	10.269%	$98.7459	$98.75	$98.75	$98.70
Purchase #6	$137.47	13.234%	$155.6628	$155.66	$155.65	$155.70
Purchase #7	$153.77	13.535%	$174.5828	$174.58	$174.60	$174.60
7 purchase totals =	$1,009.59		$1,112.4304	$1,112.42	$1,112.40	$1,112.50