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	$88.51	10.220%	$97.5557	$97.56	$97.55	$97.60
Purchase #2	$152.61	11.620%	$170.3433	$170.34	$170.35	$170.30
Purchase #3	$80.82	11.215%	$89.884	$89.88	$89.90	$89.90
Purchase #4	$220.63	8.130%	$238.5672	$238.57	$238.55	$238.60
Purchase #5	$33.35	7.388%	$35.8139	$35.81	$35.80	$35.80
Purchase #6	$29.91	6.255%	$31.7809	$31.78	$31.80	$31.80
Purchase #7	$108.77	5.685%	$114.9536	$114.95	$114.95	$115.00
7 purchase totals =	$714.60		$778.8986	$778.89	$778.90	$779.00