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	$26.39	3.734%	$27.3754	$27.38	$27.40	$27.40
Purchase #2	$98.67	7.109%	$105.6845	$105.68	$105.70	$105.70
Purchase #3	$73.41	10.148%	$80.8596	$80.86	$80.85	$80.90
Purchase #4	$42.73	4.242%	$44.5426	$44.54	$44.55	$44.50
Purchase #5	$19.46	4.742%	$20.3828	$20.38	$20.40	$20.40
Purchase #6	$103.75	11.332%	$115.507	$115.51	$115.50	$115.50
Purchase #7	$97.81	5.336%	$103.0291	$103.03	$103.05	$103.00
7 purchase totals =	$462.22		$497.3810	$497.38	$497.45	$497.40