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	$39.79	8.774%	$43.2812	$43.28	$43.30	$43.30
Purchase #2	$155.47	8.640%	$168.9026	$168.90	$168.90	$168.90
Purchase #3	$53.94	9.484%	$59.0557	$59.06	$59.05	$59.10
Purchase #4	$203.54	10.305%	$224.5148	$224.51	$224.50	$224.50
Purchase #5	$115.94	9.710%	$127.1978	$127.20	$127.20	$127.20
Purchase #6	$109.25	9.540%	$119.6725	$119.67	$119.65	$119.70
Purchase #7	$57.35	9.392%	$62.7363	$62.74	$62.75	$62.70
7 purchase totals =	$735.28		$805.3609	$805.36	$805.35	$805.40