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	$170.82	11.402%	$190.2969	$190.30	$190.30	$190.30
Purchase #2	$146.91	9.681%	$161.1324	$161.13	$161.15	$161.10
Purchase #3	$182.77	7.335%	$196.1762	$196.18	$196.20	$196.20
Purchase #4	$163.43	4.824%	$171.3139	$171.31	$171.30	$171.30
Purchase #5	$86.82	10.230%	$95.7017	$95.70	$95.70	$95.70
Purchase #6	$195.68	13.420%	$221.9403	$221.94	$221.95	$221.90
Purchase #7	$101.58	12.501%	$114.2785	$114.28	$114.30	$114.30
7 purchase totals =	$1,048.01		$1,150.8399	$1,150.84	$1,150.90	$1,150.80