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	$130.35	10.313%	$143.793	$143.79	$143.80	$143.80
Purchase #2	$112.30	9.603%	$123.0842	$123.08	$123.10	$123.10
Purchase #3	$142.98	11.260%	$159.0795	$159.08	$159.10	$159.10
Purchase #4	$221.52	7.121%	$237.2944	$237.29	$237.30	$237.30
Purchase #5	$54.43	3.831%	$56.5152	$56.52	$56.50	$56.50
Purchase #6	$41.81	6.404%	$44.4875	$44.49	$44.50	$44.50
Purchase #7	$77.28	12.507%	$86.9454	$86.95	$86.95	$86.90
7 purchase totals =	$780.67		$851.1992	$851.20	$851.25	$851.20