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	$43.72	10.681%	$48.3897	$48.39	$48.40	$48.40
Purchase #2	$107.44	6.858%	$114.8082	$114.81	$114.80	$114.80
Purchase #3	$43.41	4.306%	$45.2792	$45.28	$45.30	$45.30
Purchase #4	$208.33	9.772%	$228.688	$228.69	$228.70	$228.70
Purchase #5	$85.80	4.862%	$89.9716	$89.97	$89.95	$90.00
Purchase #6	$28.52	13.587%	$32.395	$32.40	$32.40	$32.40
Purchase #7	$78.55	10.743%	$86.9886	$86.99	$87.00	$87.00
7 purchase totals =	$595.77		$646.5203	$646.53	$646.55	$646.60