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	$134.76	5.525%	$142.2055	$142.21	$142.20	$142.20
Purchase #2	$144.72	4.106%	$150.6622	$150.66	$150.65	$150.70
Purchase #3	$162.68	11.464%	$181.3296	$181.33	$181.35	$181.30
Purchase #4	$190.62	3.217%	$196.7522	$196.75	$196.75	$196.80
Purchase #5	$86.62	4.393%	$90.4252	$90.43	$90.45	$90.40
Purchase #6	$17.80	5.759%	$18.8251	$18.83	$18.85	$18.80
Purchase #7	$88.49	13.847%	$100.7432	$100.74	$100.75	$100.70
7 purchase totals =	$825.69		$880.9430	$880.95	$881.00	$880.90