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	$181.48	10.705%	$200.9074	$200.91	$200.90	$200.90
Purchase #2	$19.46	12.590%	$21.91	$21.91	$21.90	$21.90
Purchase #3	$99.80	12.866%	$112.6403	$112.64	$112.65	$112.60
Purchase #4	$84.71	12.382%	$95.1988	$95.20	$95.20	$95.20
Purchase #5	$104.32	7.626%	$112.2754	$112.28	$112.30	$112.30
Purchase #6	$99.52	4.156%	$103.6561	$103.66	$103.65	$103.70
Purchase #7	$19.71	12.242%	$22.1229	$22.12	$22.10	$22.10
7 purchase totals =	$609.00		$668.7109	$668.72	$668.70	$668.70