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	$234.95	9.195%	$256.5537	$256.55	$256.55	$256.60
Purchase #2	$153.90	11.112%	$171.0014	$171.00	$171.00	$171.00
Purchase #3	$38.88	4.700%	$40.7074	$40.71	$40.70	$40.70
Purchase #4	$167.88	7.555%	$180.5633	$180.56	$180.55	$180.60
Purchase #5	$15.31	3.577%	$15.8576	$15.86	$15.85	$15.90
Purchase #6	$96.56	5.798%	$102.1585	$102.16	$102.15	$102.20
Purchase #7	$42.34	3.571%	$43.852	$43.85	$43.85	$43.90
7 purchase totals =	$749.82		$810.6939	$810.69	$810.65	$810.90