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	$37.84	4.385%	$39.4993	$39.50	$39.50	$39.50
Purchase #2	$193.92	12.145%	$217.4716	$217.47	$217.45	$217.50
Purchase #3	$231.48	10.751%	$256.3664	$256.37	$256.35	$256.40
Purchase #4	$86.57	7.694%	$93.2307	$93.23	$93.25	$93.20
Purchase #5	$172.90	4.718%	$181.0574	$181.06	$181.05	$181.10
Purchase #6	$117.65	11.736%	$131.4574	$131.46	$131.45	$131.50
Purchase #7	$99.60	8.826%	$108.3907	$108.39	$108.40	$108.40
7 purchase totals =	$939.96		$1,027.4735	$1,027.48	$1,027.45	$1,027.60