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	$83.72	6.602%	$89.2472	$89.25	$89.25	$89.20
Purchase #2	$224.99	7.708%	$242.3322	$242.33	$242.35	$242.30
Purchase #3	$245.48	8.390%	$266.0758	$266.08	$266.10	$266.10
Purchase #4	$22.33	11.128%	$24.8149	$24.81	$24.80	$24.80
Purchase #5	$142.77	9.475%	$156.2975	$156.30	$156.30	$156.30
Purchase #6	$136.31	11.782%	$152.37	$152.37	$152.35	$152.40
Purchase #7	$189.63	10.872%	$210.2466	$210.25	$210.25	$210.20
7 purchase totals =	$1,045.23		$1,141.3842	$1,141.39	$1,141.40	$1,141.30