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	$224.87	12.585%	$253.1699	$253.17	$253.15	$253.20
Purchase #2	$161.43	4.266%	$168.3166	$168.32	$168.30	$168.30
Purchase #3	$181.72	4.543%	$189.9755	$189.98	$190.00	$190.00
Purchase #4	$73.60	6.325%	$78.2552	$78.26	$78.25	$78.30
Purchase #5	$5.44	13.227%	$6.1595	$6.16	$6.15	$6.20
Purchase #6	$89.85	11.544%	$100.2223	$100.22	$100.20	$100.20
Purchase #7	$38.44	10.259%	$42.3836	$42.38	$42.40	$42.40
7 purchase totals =	$775.35		$838.4826	$838.49	$838.45	$838.60