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	$53.59	3.508%	$55.4699	$55.47	$55.45	$55.50
Purchase #2	$195.59	7.458%	$210.1771	$210.18	$210.20	$210.20
Purchase #3	$78.28	5.159%	$82.3185	$82.32	$82.30	$82.30
Purchase #4	$144.75	6.315%	$153.891	$153.89	$153.90	$153.90
Purchase #5	$51.58	12.333%	$57.9414	$57.94	$57.95	$57.90
Purchase #6	$63.48	7.216%	$68.0607	$68.06	$68.05	$68.10
Purchase #7	$9.45	13.413%	$10.7175	$10.72	$10.70	$10.70
7 purchase totals =	$596.72		$638.5761	$638.58	$638.55	$638.60