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	$25.81	10.322%	$28.4741	$28.47	$28.45	$28.50
Purchase #2	$80.97	10.745%	$89.6702	$89.67	$89.65	$89.70
Purchase #3	$171.68	7.580%	$184.6933	$184.69	$184.70	$184.70
Purchase #4	$161.60	5.117%	$169.8691	$169.87	$169.85	$169.90
Purchase #5	$245.27	3.613%	$254.1316	$254.13	$254.15	$254.10
Purchase #6	$69.51	9.791%	$76.3157	$76.32	$76.30	$76.30
Purchase #7	$184.69	6.370%	$196.4548	$196.45	$196.45	$196.50
7 purchase totals =	$939.53		$999.6088	$999.60	$999.55	$999.70