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	$75.29	13.840%	$85.7101	$85.71	$85.70	$85.70
Purchase #2	$85.76	7.831%	$92.4759	$92.48	$92.50	$92.50
Purchase #3	$145.76	11.456%	$162.4583	$162.46	$162.45	$162.50
Purchase #4	$178.31	6.204%	$189.3724	$189.37	$189.35	$189.40
Purchase #5	$98.96	13.165%	$111.9881	$111.99	$112.00	$112.00
Purchase #6	$144.57	9.718%	$158.6193	$158.62	$158.60	$158.60
Purchase #7	$52.56	9.200%	$57.3955	$57.40	$57.40	$57.40
7 purchase totals =	$781.21		$858.0196	$858.03	$858.00	$858.10