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	$80.90	12.860%	$91.3037	$91.30	$91.30	$91.30
Purchase #2	$166.74	12.718%	$187.946	$187.95	$187.95	$187.90
Purchase #3	$177.61	11.569%	$198.1577	$198.16	$198.15	$198.20
Purchase #4	$148.74	3.105%	$153.3584	$153.36	$153.35	$153.40
Purchase #5	$86.40	4.107%	$89.9484	$89.95	$89.95	$89.90
Purchase #6	$42.46	4.609%	$44.417	$44.42	$44.40	$44.40
Purchase #7	$148.39	10.557%	$164.0555	$164.06	$164.05	$164.10
7 purchase totals =	$851.24		$929.1867	$929.20	$929.15	$929.20