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	$19.93	7.566%	$21.4379	$21.44	$21.45	$21.40
Purchase #2	$83.28	7.615%	$89.6218	$89.62	$89.60	$89.60
Purchase #3	$28.53	8.267%	$30.8886	$30.89	$30.90	$30.90
Purchase #4	$94.69	3.586%	$98.0856	$98.09	$98.10	$98.10
Purchase #5	$197.87	9.297%	$216.266	$216.27	$216.25	$216.30
Purchase #6	$119.84	9.728%	$131.498	$131.50	$131.50	$131.50
Purchase #7	$50.84	7.726%	$54.7679	$54.77	$54.75	$54.80
7 purchase totals =	$594.98		$642.5658	$642.58	$642.55	$642.60