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	$31.42	4.637%	$32.8769	$32.88	$32.90	$32.90
Purchase #2	$73.78	6.146%	$78.3145	$78.31	$78.30	$78.30
Purchase #3	$65.94	9.326%	$72.0896	$72.09	$72.10	$72.10
Purchase #4	$241.30	7.563%	$259.5495	$259.55	$259.55	$259.50
Purchase #5	$212.35	7.816%	$228.9473	$228.95	$228.95	$228.90
Purchase #6	$191.36	12.711%	$215.6838	$215.68	$215.70	$215.70
Purchase #7	$206.95	13.142%	$234.1474	$234.15	$234.15	$234.10
7 purchase totals =	$1,023.10		$1,121.6090	$1,121.61	$1,121.65	$1,121.50