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	$86.52	4.606%	$90.5051	$90.51	$90.50	$90.50
Purchase #2	$92.78	10.710%	$102.7167	$102.72	$102.70	$102.70
Purchase #3	$232.42	4.462%	$242.7906	$242.79	$242.80	$242.80
Purchase #4	$170.68	6.379%	$181.5677	$181.57	$181.55	$181.60
Purchase #5	$246.94	7.404%	$265.2234	$265.22	$265.20	$265.20
Purchase #6	$135.71	11.499%	$151.3153	$151.32	$151.30	$151.30
Purchase #7	$39.29	12.227%	$44.094	$44.09	$44.10	$44.10
7 purchase totals =	$1,004.34		$1,078.2128	$1,078.22	$1,078.15	$1,078.20