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	$54.78	8.543%	$59.4599	$59.46	$59.45	$59.50
Purchase #2	$210.45	13.866%	$239.631	$239.63	$239.65	$239.60
Purchase #3	$89.90	5.359%	$94.7177	$94.72	$94.70	$94.70
Purchase #4	$101.25	12.831%	$114.2414	$114.24	$114.25	$114.20
Purchase #5	$44.63	5.870%	$47.2498	$47.25	$47.25	$47.20
Purchase #6	$18.61	11.562%	$20.7617	$20.76	$20.75	$20.80
Purchase #7	$64.65	12.449%	$72.6983	$72.70	$72.70	$72.70
7 purchase totals =	$584.27		$648.7598	$648.76	$648.75	$648.70