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	$238.63	6.662%	$254.5275	$254.53	$254.55	$254.50
Purchase #2	$96.72	9.135%	$105.5554	$105.56	$105.55	$105.60
Purchase #3	$124.43	5.625%	$131.4292	$131.43	$131.45	$131.40
Purchase #4	$107.72	6.851%	$115.0999	$115.10	$115.10	$115.10
Purchase #5	$196.91	6.694%	$210.0912	$210.09	$210.10	$210.10
Purchase #6	$76.59	4.574%	$80.0932	$80.09	$80.10	$80.10
Purchase #7	$91.89	5.667%	$97.0974	$97.10	$97.10	$97.10
7 purchase totals =	$932.89		$993.8938	$993.90	$993.95	$993.90