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	$110.29	13.193%	$124.8406	$124.84	$124.85	$124.80
Purchase #2	$99.85	5.122%	$104.9643	$104.96	$104.95	$105.00
Purchase #3	$54.33	13.797%	$61.8259	$61.83	$61.85	$61.80
Purchase #4	$187.30	9.874%	$205.794	$205.79	$205.80	$205.80
Purchase #5	$27.59	6.240%	$29.3116	$29.31	$29.30	$29.30
Purchase #6	$68.50	12.495%	$77.0591	$77.06	$77.05	$77.10
Purchase #7	$60.98	4.381%	$63.6515	$63.65	$63.65	$63.70
7 purchase totals =	$608.84		$667.4470	$667.44	$667.45	$667.50