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	$51.68	10.584%	$57.1498	$57.15	$57.15	$57.10
Purchase #2	$141.87	8.426%	$153.824	$153.82	$153.80	$153.80
Purchase #3	$77.30	6.260%	$82.139	$82.14	$82.15	$82.10
Purchase #4	$232.92	3.538%	$241.1607	$241.16	$241.15	$241.20
Purchase #5	$234.54	10.790%	$259.8469	$259.85	$259.85	$259.80
Purchase #6	$7.53	3.321%	$7.7801	$7.78	$7.80	$7.80
Purchase #7	$52.48	8.163%	$56.7639	$56.76	$56.75	$56.80
7 purchase totals =	$798.32		$858.6644	$858.66	$858.65	$858.60