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	$94.58	9.465%	$103.532	$103.53	$103.55	$103.50
Purchase #2	$180.32	6.339%	$191.7505	$191.75	$191.75	$191.80
Purchase #3	$100.69	10.496%	$111.2584	$111.26	$111.25	$111.30
Purchase #4	$31.69	3.145%	$32.6867	$32.69	$32.70	$32.70
Purchase #5	$26.87	11.782%	$30.0358	$30.04	$30.05	$30.00
Purchase #6	$19.46	12.625%	$21.9168	$21.92	$21.90	$21.90
Purchase #7	$26.96	6.409%	$28.6879	$28.69	$28.70	$28.70
7 purchase totals =	$480.57		$519.8681	$519.88	$519.90	$519.90