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	$13.89	3.107%	$14.3216	$14.32	$14.30	$14.30
Purchase #2	$89.85	11.821%	$100.4712	$100.47	$100.45	$100.50
Purchase #3	$84.71	5.188%	$89.1048	$89.10	$89.10	$89.10
Purchase #4	$192.86	12.500%	$216.9675	$216.97	$216.95	$217.00
Purchase #5	$99.38	10.481%	$109.796	$109.80	$109.80	$109.80
Purchase #6	$99.64	11.302%	$110.9013	$110.90	$110.90	$110.90
Purchase #7	$123.66	11.690%	$138.1159	$138.12	$138.10	$138.10
7 purchase totals =	$703.99		$779.6783	$779.68	$779.60	$779.70