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	$89.86	8.564%	$97.5556	$97.56	$97.55	$97.60
Purchase #2	$91.92	6.741%	$98.1163	$98.12	$98.10	$98.10
Purchase #3	$88.55	8.870%	$96.4044	$96.40	$96.40	$96.40
Purchase #4	$118.69	7.694%	$127.822	$127.82	$127.80	$127.80
Purchase #5	$97.37	6.269%	$103.4741	$103.47	$103.45	$103.50
Purchase #6	$179.97	10.728%	$199.2772	$199.28	$199.30	$199.30
Purchase #7	$248.25	3.643%	$257.2937	$257.29	$257.30	$257.30
7 purchase totals =	$914.61		$979.9433	$979.94	$979.90	$980.00