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	$245.67	13.568%	$279.0025	$279.00	$279.00	$279.00
Purchase #2	$143.29	11.307%	$159.4918	$159.49	$159.50	$159.50
Purchase #3	$21.38	5.143%	$22.4796	$22.48	$22.50	$22.50
Purchase #4	$119.33	3.553%	$123.5698	$123.57	$123.55	$123.60
Purchase #5	$212.31	12.402%	$238.6407	$238.64	$238.65	$238.60
Purchase #6	$37.73	6.855%	$40.3164	$40.32	$40.30	$40.30
Purchase #7	$240.65	3.121%	$248.1607	$248.16	$248.15	$248.20
7 purchase totals =	$1,020.36		$1,111.6615	$1,111.66	$1,111.65	$1,111.70