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	$53.32	3.486%	$55.1787	$55.18	$55.20	$55.20
Purchase #2	$58.58	7.466%	$62.9536	$62.95	$62.95	$63.00
Purchase #3	$103.27	10.408%	$114.0183	$114.02	$114.00	$114.00
Purchase #4	$79.73	4.591%	$83.3904	$83.39	$83.40	$83.40
Purchase #5	$73.59	11.841%	$82.3038	$82.30	$82.30	$82.30
Purchase #6	$74.85	4.784%	$78.4308	$78.43	$78.45	$78.40
Purchase #7	$156.83	11.350%	$174.6302	$174.63	$174.65	$174.60
7 purchase totals =	$600.17		$650.9058	$650.90	$650.95	$650.90