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	$228.53	9.351%	$249.8998	$249.90	$249.90	$249.90
Purchase #2	$237.74	8.320%	$257.52	$257.52	$257.50	$257.50
Purchase #3	$15.96	12.631%	$17.9759	$17.98	$18.00	$18.00
Purchase #4	$232.59	7.520%	$250.0808	$250.08	$250.10	$250.10
Purchase #5	$115.74	9.755%	$127.0304	$127.03	$127.05	$127.00
Purchase #6	$58.69	5.310%	$61.8064	$61.81	$61.80	$61.80
Purchase #7	$126.86	7.598%	$136.4988	$136.50	$136.50	$136.50
7 purchase totals =	$1,016.11		$1,100.8121	$1,100.82	$1,100.85	$1,100.80