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	$74.56	5.759%	$78.8539	$78.85	$78.85	$78.90
Purchase #2	$111.41	9.731%	$122.2513	$122.25	$122.25	$122.30
Purchase #3	$89.96	3.200%	$92.8387	$92.84	$92.85	$92.80
Purchase #4	$149.49	13.598%	$169.8177	$169.82	$169.80	$169.80
Purchase #5	$100.68	11.277%	$112.0337	$112.03	$112.05	$112.00
Purchase #6	$134.46	10.402%	$148.4465	$148.45	$148.45	$148.40
Purchase #7	$99.33	6.137%	$105.4259	$105.43	$105.45	$105.40
7 purchase totals =	$759.89		$829.6677	$829.67	$829.70	$829.60