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	$26.27	6.118%	$27.8772	$27.88	$27.90	$27.90
Purchase #2	$61.47	13.634%	$69.8508	$69.85	$69.85	$69.90
Purchase #3	$78.90	5.539%	$83.2703	$83.27	$83.25	$83.30
Purchase #4	$73.80	4.147%	$76.8605	$76.86	$76.85	$76.90
Purchase #5	$228.47	7.769%	$246.2198	$246.22	$246.20	$246.20
Purchase #6	$99.40	10.397%	$109.7346	$109.73	$109.75	$109.70
Purchase #7	$25.85	9.380%	$28.2747	$28.27	$28.25	$28.30
7 purchase totals =	$594.16		$642.0879	$642.08	$642.05	$642.20