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	$235.87	12.690%	$265.8019	$265.80	$265.80	$265.80
Purchase #2	$73.75	6.416%	$78.4818	$78.48	$78.50	$78.50
Purchase #3	$97.97	12.537%	$110.2525	$110.25	$110.25	$110.30
Purchase #4	$55.26	13.646%	$62.8008	$62.80	$62.80	$62.80
Purchase #5	$27.32	5.126%	$28.7204	$28.72	$28.70	$28.70
Purchase #6	$51.30	6.454%	$54.6109	$54.61	$54.60	$54.60
Purchase #7	$98.70	7.287%	$105.8923	$105.89	$105.90	$105.90
7 purchase totals =	$640.17		$706.5606	$706.55	$706.55	$706.60