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	$53.51	5.601%	$56.5071	$56.51	$56.50	$56.50
Purchase #2	$226.46	10.218%	$249.5997	$249.60	$249.60	$249.60
Purchase #3	$227.34	10.108%	$250.3195	$250.32	$250.30	$250.30
Purchase #4	$160.47	4.256%	$167.2996	$167.30	$167.30	$167.30
Purchase #5	$82.77	9.599%	$90.7151	$90.72	$90.70	$90.70
Purchase #6	$162.97	6.353%	$173.3235	$173.32	$173.30	$173.30
Purchase #7	$225.38	10.441%	$248.9119	$248.91	$248.90	$248.90
7 purchase totals =	$1,138.90		$1,236.6764	$1,236.68	$1,236.60	$1,236.60