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	$229.76	4.708%	$240.5771	$240.58	$240.60	$240.60
Purchase #2	$228.59	13.732%	$259.98	$259.98	$260.00	$260.00
Purchase #3	$43.72	13.588%	$49.6607	$49.66	$49.65	$49.70
Purchase #4	$141.82	8.278%	$153.5599	$153.56	$153.55	$153.60
Purchase #5	$113.59	8.632%	$123.3951	$123.40	$123.40	$123.40
Purchase #6	$71.31	11.427%	$79.4586	$79.46	$79.45	$79.50
Purchase #7	$181.96	5.139%	$191.3109	$191.31	$191.30	$191.30
7 purchase totals =	$1,010.75		$1,097.9423	$1,097.95	$1,097.95	$1,098.10