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	$108.67	6.641%	$115.8868	$115.89	$115.90	$115.90
Purchase #2	$124.45	10.365%	$137.3492	$137.35	$137.35	$137.30
Purchase #3	$241.51	8.234%	$261.3959	$261.40	$261.40	$261.40
Purchase #4	$136.97	4.410%	$143.0104	$143.01	$143.00	$143.00
Purchase #5	$181.30	8.271%	$196.2953	$196.30	$196.30	$196.30
Purchase #6	$74.44	10.392%	$82.1758	$82.18	$82.20	$82.20
Purchase #7	$65.69	9.568%	$71.9752	$71.98	$72.00	$72.00
7 purchase totals =	$933.03		$1,008.0886	$1,008.11	$1,008.15	$1,008.10