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	$13.87	3.527%	$14.3592	$14.36	$14.35	$14.40
Purchase #2	$119.56	12.822%	$134.89	$134.89	$134.90	$134.90
Purchase #3	$59.49	6.736%	$63.4972	$63.50	$63.50	$63.50
Purchase #4	$82.74	9.588%	$90.6731	$90.67	$90.65	$90.70
Purchase #5	$139.94	13.695%	$159.1048	$159.10	$159.10	$159.10
Purchase #6	$39.57	9.221%	$43.2187	$43.22	$43.20	$43.20
Purchase #7	$113.44	13.604%	$128.8724	$128.87	$128.85	$128.90
7 purchase totals =	$568.61		$634.6154	$634.61	$634.55	$634.70