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	$22.75	7.779%	$24.5197	$24.52	$24.50	$24.50
Purchase #2	$31.43	3.112%	$32.4081	$32.41	$32.40	$32.40
Purchase #3	$109.98	5.796%	$116.3544	$116.35	$116.35	$116.40
Purchase #4	$118.42	7.671%	$127.504	$127.50	$127.50	$127.50
Purchase #5	$139.88	8.696%	$152.044	$152.04	$152.05	$152.00
Purchase #6	$102.58	6.410%	$109.1554	$109.16	$109.15	$109.20
Purchase #7	$170.73	7.832%	$184.1016	$184.10	$184.10	$184.10
7 purchase totals =	$695.77		$746.0872	$746.08	$746.05	$746.10