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	$77.82	9.305%	$85.0612	$85.06	$85.05	$85.10
Purchase #2	$53.64	11.407%	$59.7587	$59.76	$59.75	$59.80
Purchase #3	$56.53	5.370%	$59.5657	$59.57	$59.55	$59.60
Purchase #4	$93.83	11.641%	$104.7528	$104.75	$104.75	$104.80
Purchase #5	$27.68	3.270%	$28.5851	$28.59	$28.60	$28.60
Purchase #6	$98.52	9.573%	$107.9513	$107.95	$107.95	$108.00
Purchase #7	$181.42	9.578%	$198.7964	$198.80	$198.80	$198.80
7 purchase totals =	$589.44		$644.4712	$644.48	$644.45	$644.70