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	$222.27	12.294%	$249.5959	$249.60	$249.60	$249.60
Purchase #2	$24.26	12.310%	$27.2464	$27.25	$27.25	$27.20
Purchase #3	$145.45	11.667%	$162.4197	$162.42	$162.40	$162.40
Purchase #4	$133.40	12.546%	$150.1364	$150.14	$150.15	$150.10
Purchase #5	$68.37	4.270%	$71.2894	$71.29	$71.30	$71.30
Purchase #6	$51.85	3.700%	$53.7685	$53.77	$53.75	$53.80
Purchase #7	$106.43	3.243%	$109.8815	$109.88	$109.90	$109.90
7 purchase totals =	$752.03		$824.3378	$824.35	$824.35	$824.30