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	$79.69	12.520%	$89.6672	$89.67	$89.65	$89.70
Purchase #2	$179.87	4.827%	$188.5523	$188.55	$188.55	$188.60
Purchase #3	$236.70	7.820%	$255.2099	$255.21	$255.20	$255.20
Purchase #4	$26.34	3.872%	$27.3599	$27.36	$27.35	$27.40
Purchase #5	$108.88	4.844%	$114.1541	$114.15	$114.15	$114.20
Purchase #6	$54.71	8.709%	$59.4747	$59.47	$59.45	$59.50
Purchase #7	$214.56	12.453%	$241.2792	$241.28	$241.30	$241.30
7 purchase totals =	$900.75		$975.6973	$975.69	$975.65	$975.90