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	$5.79	7.225%	$6.2083	$6.21	$6.20	$6.20
Purchase #2	$160.25	13.316%	$181.5889	$181.59	$181.60	$181.60
Purchase #3	$59.92	9.392%	$65.5477	$65.55	$65.55	$65.50
Purchase #4	$19.46	8.465%	$21.1073	$21.11	$21.10	$21.10
Purchase #5	$112.50	5.402%	$118.5773	$118.58	$118.60	$118.60
Purchase #6	$38.30	12.326%	$43.0209	$43.02	$43.00	$43.00
Purchase #7	$229.69	9.222%	$250.872	$250.87	$250.85	$250.90
7 purchase totals =	$625.91		$686.9224	$686.93	$686.90	$686.90