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	$114.97	12.615%	$129.4735	$129.47	$129.45	$129.50
Purchase #2	$132.75	12.720%	$149.6358	$149.64	$149.65	$149.60
Purchase #3	$13.84	8.605%	$15.0309	$15.03	$15.05	$15.00
Purchase #4	$156.80	9.361%	$171.478	$171.48	$171.50	$171.50
Purchase #5	$57.50	3.122%	$59.2952	$59.30	$59.30	$59.30
Purchase #6	$248.59	12.416%	$279.4549	$279.45	$279.45	$279.50
Purchase #7	$54.69	9.151%	$59.6947	$59.69	$59.70	$59.70
7 purchase totals =	$779.14		$864.0630	$864.06	$864.10	$864.10