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	$139.63	4.420%	$145.8016	$145.80	$145.80	$145.80
Purchase #2	$81.82	12.234%	$91.8299	$91.83	$91.85	$91.80
Purchase #3	$247.76	13.231%	$280.5411	$280.54	$280.55	$280.50
Purchase #4	$225.89	12.235%	$253.5276	$253.53	$253.55	$253.50
Purchase #5	$39.88	6.786%	$42.5863	$42.59	$42.60	$42.60
Purchase #6	$221.99	7.199%	$237.9711	$237.97	$237.95	$238.00
Purchase #7	$18.69	9.295%	$20.4272	$20.43	$20.45	$20.40
7 purchase totals =	$975.66		$1,072.6848	$1,072.69	$1,072.75	$1,072.60