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	$73.60	8.517%	$79.8685	$79.87	$79.85	$79.90
Purchase #2	$184.29	6.496%	$196.2615	$196.26	$196.25	$196.30
Purchase #3	$149.45	3.225%	$154.2698	$154.27	$154.25	$154.30
Purchase #4	$187.27	6.311%	$199.0886	$199.09	$199.10	$199.10
Purchase #5	$89.61	9.708%	$98.3093	$98.31	$98.30	$98.30
Purchase #6	$6.96	8.823%	$7.5741	$7.57	$7.55	$7.60
Purchase #7	$165.52	8.338%	$179.3211	$179.32	$179.30	$179.30
7 purchase totals =	$856.70		$914.6929	$914.69	$914.60	$914.80