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	$54.45	4.457%	$56.8768	$56.88	$56.90	$56.90
Purchase #2	$19.81	13.292%	$22.4431	$22.44	$22.45	$22.40
Purchase #3	$121.77	5.380%	$128.3212	$128.32	$128.30	$128.30
Purchase #4	$74.89	9.848%	$82.2652	$82.27	$82.25	$82.30
Purchase #5	$16.33	9.372%	$17.8604	$17.86	$17.85	$17.90
Purchase #6	$176.47	12.858%	$199.1605	$199.16	$199.15	$199.20
Purchase #7	$130.73	8.824%	$142.2656	$142.27	$142.25	$142.30
7 purchase totals =	$594.45		$649.1928	$649.20	$649.15	$649.30