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	$154.50	7.810%	$166.5665	$166.57	$166.55	$166.60
Purchase #2	$207.38	6.689%	$221.2516	$221.25	$221.25	$221.30
Purchase #3	$54.53	11.164%	$60.6177	$60.62	$60.60	$60.60
Purchase #4	$137.79	4.131%	$143.4821	$143.48	$143.50	$143.50
Purchase #5	$155.74	9.323%	$170.2596	$170.26	$170.25	$170.30
Purchase #6	$43.46	4.724%	$45.5131	$45.51	$45.50	$45.50
Purchase #7	$239.83	4.323%	$250.1979	$250.20	$250.20	$250.20
7 purchase totals =	$993.23		$1,057.8885	$1,057.89	$1,057.85	$1,058.00