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	$176.51	12.246%	$198.1254	$198.13	$198.15	$198.10
Purchase #2	$87.26	3.210%	$90.061	$90.06	$90.05	$90.10
Purchase #3	$82.72	8.424%	$89.6883	$89.69	$89.70	$89.70
Purchase #4	$111.95	10.197%	$123.3655	$123.37	$123.35	$123.40
Purchase #5	$218.89	8.449%	$237.384	$237.38	$237.40	$237.40
Purchase #6	$242.90	5.218%	$255.5745	$255.57	$255.55	$255.60
Purchase #7	$5.58	12.839%	$6.2964	$6.30	$6.30	$6.30
7 purchase totals =	$925.81		$1,000.4951	$1,000.50	$1,000.50	$1,000.60