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	$90.72	8.381%	$98.3232	$98.32	$98.30	$98.30
Purchase #2	$91.53	7.406%	$98.3087	$98.31	$98.30	$98.30
Purchase #3	$213.51	6.476%	$227.3369	$227.34	$227.35	$227.30
Purchase #4	$11.73	13.542%	$13.3185	$13.32	$13.30	$13.30
Purchase #5	$47.26	7.612%	$50.8574	$50.86	$50.85	$50.90
Purchase #6	$39.90	5.400%	$42.0546	$42.05	$42.05	$42.10
Purchase #7	$87.42	11.803%	$97.7382	$97.74	$97.75	$97.70
7 purchase totals =	$582.07		$627.9375	$627.94	$627.90	$627.90