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	$139.82	5.577%	$147.6178	$147.62	$147.60	$147.60
Purchase #2	$104.57	4.565%	$109.3436	$109.34	$109.35	$109.30
Purchase #3	$79.75	11.752%	$89.1222	$89.12	$89.10	$89.10
Purchase #4	$94.85	10.781%	$105.0758	$105.08	$105.10	$105.10
Purchase #5	$240.82	13.126%	$272.43	$272.43	$272.45	$272.40
Purchase #6	$146.31	8.249%	$158.3791	$158.38	$158.40	$158.40
Purchase #7	$6.36	8.387%	$6.8934	$6.89	$6.90	$6.90
7 purchase totals =	$812.48		$888.8619	$888.86	$888.90	$888.80