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	$21.73	10.613%	$24.0362	$24.04	$24.05	$24.00
Purchase #2	$69.62	3.628%	$72.1458	$72.15	$72.15	$72.10
Purchase #3	$62.67	11.247%	$69.7185	$69.72	$69.70	$69.70
Purchase #4	$36.64	3.498%	$37.9217	$37.92	$37.90	$37.90
Purchase #5	$237.52	10.775%	$263.1128	$263.11	$263.10	$263.10
Purchase #6	$87.65	12.169%	$98.3161	$98.32	$98.30	$98.30
Purchase #7	$79.59	4.109%	$82.8604	$82.86	$82.85	$82.90
7 purchase totals =	$595.42		$648.1115	$648.12	$648.05	$648.00