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	$115.80	10.108%	$127.5051	$127.51	$127.50	$127.50
Purchase #2	$64.26	8.151%	$69.4978	$69.50	$69.50	$69.50
Purchase #3	$104.89	5.695%	$110.8635	$110.86	$110.85	$110.90
Purchase #4	$100.72	3.595%	$104.3409	$104.34	$104.35	$104.30
Purchase #5	$65.86	8.629%	$71.5431	$71.54	$71.55	$71.50
Purchase #6	$109.49	6.432%	$116.5324	$116.53	$116.55	$116.50
Purchase #7	$184.38	11.453%	$205.497	$205.50	$205.50	$205.50
7 purchase totals =	$745.40		$805.7798	$805.78	$805.80	$805.70