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	$75.38	5.557%	$79.5689	$79.57	$79.55	$79.60
Purchase #2	$164.34	4.254%	$171.331	$171.33	$171.35	$171.30
Purchase #3	$53.94	8.229%	$58.3787	$58.38	$58.40	$58.40
Purchase #4	$53.54	11.497%	$59.6955	$59.70	$59.70	$59.70
Purchase #5	$230.66	5.376%	$243.0603	$243.06	$243.05	$243.10
Purchase #6	$81.96	9.139%	$89.4503	$89.45	$89.45	$89.50
Purchase #7	$232.42	11.151%	$258.3372	$258.34	$258.35	$258.30
7 purchase totals =	$892.24		$959.8219	$959.83	$959.85	$959.90