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	$35.28	10.658%	$39.0401	$39.04	$39.05	$39.00
Purchase #2	$56.91	6.172%	$60.4225	$60.42	$60.40	$60.40
Purchase #3	$86.82	9.668%	$95.2138	$95.21	$95.20	$95.20
Purchase #4	$41.74	6.844%	$44.5967	$44.60	$44.60	$44.60
Purchase #5	$119.68	3.344%	$123.6821	$123.68	$123.70	$123.70
Purchase #6	$116.44	9.818%	$127.8721	$127.87	$127.85	$127.90
Purchase #7	$236.94	13.787%	$269.6069	$269.61	$269.60	$269.60
7 purchase totals =	$693.81		$760.4342	$760.43	$760.40	$760.40