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	$6.30	3.467%	$6.5184	$6.52	$6.50	$6.50
Purchase #2	$179.72	5.464%	$189.5399	$189.54	$189.55	$189.50
Purchase #3	$56.39	5.503%	$59.4931	$59.49	$59.50	$59.50
Purchase #4	$16.77	6.551%	$17.8686	$17.87	$17.85	$17.90
Purchase #5	$38.35	8.393%	$41.5687	$41.57	$41.55	$41.60
Purchase #6	$84.75	8.571%	$92.0139	$92.01	$92.00	$92.00
Purchase #7	$238.56	7.441%	$256.3112	$256.31	$256.30	$256.30
7 purchase totals =	$620.84		$663.3138	$663.31	$663.25	$663.30