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	$72.84	8.473%	$79.0117	$79.01	$79.00	$79.00
Purchase #2	$50.97	13.127%	$57.6608	$57.66	$57.65	$57.70
Purchase #3	$172.58	13.708%	$196.2373	$196.24	$196.25	$196.20
Purchase #4	$105.35	12.842%	$118.879	$118.88	$118.90	$118.90
Purchase #5	$106.45	7.585%	$114.5242	$114.52	$114.50	$114.50
Purchase #6	$63.55	13.791%	$72.3142	$72.31	$72.30	$72.30
Purchase #7	$82.84	8.220%	$89.6494	$89.65	$89.65	$89.60
7 purchase totals =	$654.58		$728.2766	$728.27	$728.25	$728.20