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	$76.68	8.739%	$83.3811	$83.38	$83.40	$83.40
Purchase #2	$53.83	11.287%	$59.9058	$59.91	$59.90	$59.90
Purchase #3	$6.55	10.681%	$7.2496	$7.25	$7.25	$7.20
Purchase #4	$30.96	4.301%	$32.2916	$32.29	$32.30	$32.30
Purchase #5	$226.67	3.822%	$235.3333	$235.33	$235.35	$235.30
Purchase #6	$121.58	8.863%	$132.3556	$132.36	$132.35	$132.40
Purchase #7	$102.64	9.141%	$112.0223	$112.02	$112.00	$112.00
7 purchase totals =	$618.91		$662.5393	$662.54	$662.55	$662.50