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	$244.38	12.866%	$275.8219	$275.82	$275.80	$275.80
Purchase #2	$89.69	8.183%	$97.0293	$97.03	$97.05	$97.00
Purchase #3	$139.48	10.652%	$154.3374	$154.34	$154.35	$154.30
Purchase #4	$136.27	4.216%	$142.0151	$142.02	$142.00	$142.00
Purchase #5	$168.44	9.565%	$184.5513	$184.55	$184.55	$184.60
Purchase #6	$17.89	5.209%	$18.8219	$18.82	$18.80	$18.80
Purchase #7	$210.63	4.103%	$219.2721	$219.27	$219.25	$219.30
7 purchase totals =	$1,006.78		$1,091.8490	$1,091.85	$1,091.80	$1,091.80