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	$159.78	8.714%	$173.7032	$173.70	$173.70	$173.70
Purchase #2	$81.56	11.510%	$90.9476	$90.95	$90.95	$90.90
Purchase #3	$219.47	9.517%	$240.357	$240.36	$240.35	$240.40
Purchase #4	$181.96	4.848%	$190.7814	$190.78	$190.80	$190.80
Purchase #5	$234.51	11.534%	$261.5584	$261.56	$261.55	$261.60
Purchase #6	$232.88	7.372%	$250.0479	$250.05	$250.05	$250.00
Purchase #7	$80.82	10.591%	$89.3796	$89.38	$89.40	$89.40
7 purchase totals =	$1,190.98		$1,296.7751	$1,296.78	$1,296.80	$1,296.80