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	$226.81	12.392%	$254.9163	$254.92	$254.90	$254.90
Purchase #2	$147.66	4.462%	$154.2486	$154.25	$154.25	$154.20
Purchase #3	$77.51	11.132%	$86.1384	$86.14	$86.15	$86.10
Purchase #4	$53.36	12.287%	$59.9163	$59.92	$59.90	$59.90
Purchase #5	$45.40	4.214%	$47.3132	$47.31	$47.30	$47.30
Purchase #6	$90.38	12.536%	$101.71	$101.71	$101.70	$101.70
Purchase #7	$139.68	13.273%	$158.2197	$158.22	$158.20	$158.20
7 purchase totals =	$780.80		$862.4625	$862.47	$862.40	$862.30