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	$35.38	11.234%	$39.3546	$39.35	$39.35	$39.40
Purchase #2	$57.41	13.427%	$65.1184	$65.12	$65.10	$65.10
Purchase #3	$123.58	3.805%	$128.2822	$128.28	$128.30	$128.30
Purchase #4	$56.66	9.190%	$61.8671	$61.87	$61.85	$61.90
Purchase #5	$171.61	11.441%	$191.2439	$191.24	$191.25	$191.20
Purchase #6	$99.57	3.233%	$102.7891	$102.79	$102.80	$102.80
Purchase #7	$100.56	3.821%	$104.4024	$104.40	$104.40	$104.40
7 purchase totals =	$644.77		$693.0577	$693.05	$693.05	$693.10