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	$29.99	5.530%	$31.6484	$31.65	$31.65	$31.60
Purchase #2	$80.63	7.245%	$86.4716	$86.47	$86.45	$86.50
Purchase #3	$42.44	6.806%	$45.3285	$45.33	$45.35	$45.30
Purchase #4	$128.94	5.706%	$136.2973	$136.30	$136.30	$136.30
Purchase #5	$203.56	3.656%	$211.0022	$211.00	$211.00	$211.00
Purchase #6	$94.51	5.709%	$99.9056	$99.91	$99.90	$99.90
Purchase #7	$66.43	12.478%	$74.7191	$74.72	$74.70	$74.70
7 purchase totals =	$646.50		$685.3727	$685.38	$685.35	$685.30