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	$96.35	3.384%	$99.6105	$99.61	$99.60	$99.60
Purchase #2	$114.76	11.260%	$127.682	$127.68	$127.70	$127.70
Purchase #3	$108.47	11.534%	$120.9809	$120.98	$121.00	$121.00
Purchase #4	$147.60	11.670%	$164.8249	$164.82	$164.80	$164.80
Purchase #5	$82.48	5.194%	$86.764	$86.76	$86.75	$86.80
Purchase #6	$57.73	12.728%	$65.0779	$65.08	$65.10	$65.10
Purchase #7	$233.62	5.175%	$245.7098	$245.71	$245.70	$245.70
7 purchase totals =	$841.01		$910.6500	$910.64	$910.65	$910.70