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	$168.39	7.550%	$181.1034	$181.10	$181.10	$181.10
Purchase #2	$131.33	6.444%	$139.7929	$139.79	$139.80	$139.80
Purchase #3	$142.79	12.223%	$160.2432	$160.24	$160.25	$160.20
Purchase #4	$162.33	6.270%	$172.5081	$172.51	$172.50	$172.50
Purchase #5	$85.80	12.854%	$96.8287	$96.83	$96.85	$96.80
Purchase #6	$7.49	7.863%	$8.0789	$8.08	$8.10	$8.10
Purchase #7	$98.58	12.708%	$111.1075	$111.11	$111.10	$111.10
7 purchase totals =	$796.71		$869.6627	$869.66	$869.70	$869.60