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	$234.83	13.600%	$266.7669	$266.77	$266.75	$266.80
Purchase #2	$27.92	12.196%	$31.3251	$31.33	$31.35	$31.30
Purchase #3	$133.91	13.556%	$152.0628	$152.06	$152.05	$152.10
Purchase #4	$123.45	11.730%	$137.9307	$137.93	$137.95	$137.90
Purchase #5	$72.37	12.637%	$81.5154	$81.52	$81.50	$81.50
Purchase #6	$27.53	12.109%	$30.8636	$30.86	$30.85	$30.90
Purchase #7	$123.78	12.828%	$139.6585	$139.66	$139.65	$139.70
7 purchase totals =	$743.79		$840.1230	$840.13	$840.10	$840.20