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	$68.72	13.380%	$77.9147	$77.91	$77.90	$77.90
Purchase #2	$98.38	13.664%	$111.8226	$111.82	$111.80	$111.80
Purchase #3	$150.48	7.102%	$161.1671	$161.17	$161.15	$161.20
Purchase #4	$223.31	12.110%	$250.3528	$250.35	$250.35	$250.40
Purchase #5	$107.77	6.481%	$114.7546	$114.75	$114.75	$114.80
Purchase #6	$148.43	12.177%	$166.5043	$166.50	$166.50	$166.50
Purchase #7	$181.25	9.501%	$198.4706	$198.47	$198.45	$198.50
7 purchase totals =	$978.34		$1,080.9867	$1,080.97	$1,080.90	$1,081.10