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	$73.88	7.820%	$79.6574	$79.66	$79.65	$79.70
Purchase #2	$145.73	10.426%	$160.9238	$160.92	$160.90	$160.90
Purchase #3	$35.80	10.637%	$39.608	$39.61	$39.60	$39.60
Purchase #4	$33.96	10.465%	$37.5139	$37.51	$37.50	$37.50
Purchase #5	$238.85	8.802%	$259.8736	$259.87	$259.85	$259.90
Purchase #6	$16.56	10.377%	$18.2784	$18.28	$18.30	$18.30
Purchase #7	$25.75	7.656%	$27.7214	$27.72	$27.70	$27.70
7 purchase totals =	$570.53		$623.5765	$623.57	$623.50	$623.60