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	$130.95	9.652%	$143.5893	$143.59	$143.60	$143.60
Purchase #2	$109.50	6.695%	$116.831	$116.83	$116.85	$116.80
Purchase #3	$155.34	13.158%	$175.7796	$175.78	$175.80	$175.80
Purchase #4	$183.78	11.608%	$205.1132	$205.11	$205.10	$205.10
Purchase #5	$43.85	8.571%	$47.6084	$47.61	$47.60	$47.60
Purchase #6	$107.82	3.796%	$111.9128	$111.91	$111.90	$111.90
Purchase #7	$68.43	5.128%	$71.9391	$71.94	$71.95	$71.90
7 purchase totals =	$799.67		$872.7734	$872.77	$872.80	$872.70