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	$45.62	3.751%	$47.3312	$47.33	$47.35	$47.30
Purchase #2	$32.88	12.838%	$37.1011	$37.10	$37.10	$37.10
Purchase #3	$107.90	10.187%	$118.8918	$118.89	$118.90	$118.90
Purchase #4	$70.40	13.740%	$80.073	$80.07	$80.05	$80.10
Purchase #5	$71.45	5.526%	$75.3983	$75.40	$75.40	$75.40
Purchase #6	$90.78	4.563%	$94.9223	$94.92	$94.90	$94.90
Purchase #7	$170.94	8.419%	$185.3314	$185.33	$185.35	$185.30
7 purchase totals =	$589.97		$639.0491	$639.04	$639.05	$639.00