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	$55.82	6.357%	$59.3685	$59.37	$59.35	$59.40
Purchase #2	$191.88	5.373%	$202.1897	$202.19	$202.20	$202.20
Purchase #3	$92.78	6.816%	$99.1039	$99.10	$99.10	$99.10
Purchase #4	$61.30	8.704%	$66.6356	$66.64	$66.65	$66.60
Purchase #5	$77.80	13.402%	$88.2268	$88.23	$88.25	$88.20
Purchase #6	$38.41	10.780%	$42.5506	$42.55	$42.55	$42.60
Purchase #7	$57.42	3.323%	$59.3281	$59.33	$59.35	$59.30
7 purchase totals =	$575.41		$617.4032	$617.41	$617.45	$617.40