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	$159.33	13.758%	$181.2506	$181.25	$181.25	$181.30
Purchase #2	$40.25	9.615%	$44.12	$44.12	$44.10	$44.10
Purchase #3	$104.40	7.588%	$112.3219	$112.32	$112.30	$112.30
Purchase #4	$170.54	5.218%	$179.4388	$179.44	$179.45	$179.40
Purchase #5	$196.27	10.271%	$216.4289	$216.43	$216.45	$216.40
Purchase #6	$177.89	7.307%	$190.8884	$190.89	$190.90	$190.90
Purchase #7	$183.53	12.129%	$205.7904	$205.79	$205.80	$205.80
7 purchase totals =	$1,032.21		$1,130.2390	$1,130.24	$1,130.25	$1,130.20