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	$71.77	10.695%	$79.4458	$79.45	$79.45	$79.40
Purchase #2	$107.59	3.373%	$111.219	$111.22	$111.20	$111.20
Purchase #3	$136.41	13.364%	$154.6398	$154.64	$154.65	$154.60
Purchase #4	$169.79	6.627%	$181.042	$181.04	$181.05	$181.00
Purchase #5	$85.99	4.489%	$89.8501	$89.85	$89.85	$89.90
Purchase #6	$44.39	13.107%	$50.2082	$50.21	$50.20	$50.20
Purchase #7	$222.31	8.151%	$240.4305	$240.43	$240.45	$240.40
7 purchase totals =	$838.25		$906.8354	$906.84	$906.85	$906.70