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	$93.35	12.821%	$105.3184	$105.32	$105.30	$105.30
Purchase #2	$131.95	10.351%	$145.6081	$145.61	$145.60	$145.60
Purchase #3	$111.61	7.842%	$120.3625	$120.36	$120.35	$120.40
Purchase #4	$59.82	4.820%	$62.7033	$62.70	$62.70	$62.70
Purchase #5	$92.65	11.408%	$103.2195	$103.22	$103.20	$103.20
Purchase #6	$239.62	8.459%	$259.8895	$259.89	$259.90	$259.90
Purchase #7	$69.85	10.592%	$77.2485	$77.25	$77.25	$77.20
7 purchase totals =	$798.85		$874.3498	$874.35	$874.30	$874.30