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	$14.64	6.435%	$15.5821	$15.58	$15.60	$15.60
Purchase #2	$82.57	8.826%	$89.8576	$89.86	$89.85	$89.90
Purchase #3	$126.42	5.605%	$133.5058	$133.51	$133.50	$133.50
Purchase #4	$245.78	9.373%	$268.817	$268.82	$268.80	$268.80
Purchase #5	$112.51	10.361%	$124.1672	$124.17	$124.15	$124.20
Purchase #6	$157.30	9.251%	$171.8518	$171.85	$171.85	$171.90
Purchase #7	$39.70	12.409%	$44.6264	$44.63	$44.65	$44.60
7 purchase totals =	$778.92		$848.4079	$848.42	$848.40	$848.50