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	$158.80	10.202%	$175.0008	$175.00	$175.00	$175.00
Purchase #2	$230.98	3.306%	$238.6162	$238.62	$238.60	$238.60
Purchase #3	$218.45	7.255%	$234.2985	$234.30	$234.30	$234.30
Purchase #4	$11.73	10.526%	$12.9647	$12.96	$12.95	$13.00
Purchase #5	$132.48	10.138%	$145.9108	$145.91	$145.90	$145.90
Purchase #6	$203.96	5.561%	$215.3022	$215.30	$215.30	$215.30
Purchase #7	$74.27	5.334%	$78.2316	$78.23	$78.25	$78.20
7 purchase totals =	$1,030.67		$1,100.3248	$1,100.32	$1,100.30	$1,100.30