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	$57.71	13.514%	$65.5089	$65.51	$65.50	$65.50
Purchase #2	$103.69	13.417%	$117.6021	$117.60	$117.60	$117.60
Purchase #3	$213.26	4.245%	$222.3129	$222.31	$222.30	$222.30
Purchase #4	$55.90	9.812%	$61.3849	$61.38	$61.40	$61.40
Purchase #5	$154.47	8.462%	$167.5413	$167.54	$167.55	$167.50
Purchase #6	$234.35	3.489%	$242.5265	$242.53	$242.55	$242.50
Purchase #7	$62.83	4.337%	$65.5549	$65.55	$65.55	$65.60
7 purchase totals =	$882.21		$942.4315	$942.42	$942.45	$942.40