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	$22.73	5.221%	$23.9167	$23.92	$23.90	$23.90
Purchase #2	$125.42	11.726%	$140.1267	$140.13	$140.15	$140.10
Purchase #3	$95.39	4.434%	$99.6196	$99.62	$99.60	$99.60
Purchase #4	$98.53	6.506%	$104.9404	$104.94	$104.95	$104.90
Purchase #5	$62.51	11.543%	$69.7255	$69.73	$69.75	$69.70
Purchase #6	$27.83	5.365%	$29.3231	$29.32	$29.30	$29.30
Purchase #7	$32.61	3.376%	$33.7109	$33.71	$33.70	$33.70
7 purchase totals =	$465.02		$501.3629	$501.37	$501.35	$501.20