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	$226.44	5.704%	$239.3561	$239.36	$239.35	$239.40
Purchase #2	$197.72	11.816%	$221.0826	$221.08	$221.10	$221.10
Purchase #3	$64.29	13.191%	$72.7705	$72.77	$72.75	$72.80
Purchase #4	$86.32	3.337%	$89.2005	$89.20	$89.20	$89.20
Purchase #5	$94.97	8.499%	$103.0415	$103.04	$103.05	$103.00
Purchase #6	$17.26	4.619%	$18.0572	$18.06	$18.05	$18.10
Purchase #7	$85.36	4.629%	$89.3113	$89.31	$89.30	$89.30
7 purchase totals =	$772.36		$832.8197	$832.82	$832.80	$832.90