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	$245.87	9.189%	$268.463	$268.46	$268.45	$268.50
Purchase #2	$232.86	5.549%	$245.7814	$245.78	$245.80	$245.80
Purchase #3	$190.70	10.529%	$210.7788	$210.78	$210.80	$210.80
Purchase #4	$44.98	7.632%	$48.4129	$48.41	$48.40	$48.40
Purchase #5	$35.83	12.496%	$40.3073	$40.31	$40.30	$40.30
Purchase #6	$61.69	11.649%	$68.8763	$68.88	$68.90	$68.90
Purchase #7	$106.84	12.464%	$120.1565	$120.16	$120.15	$120.20
7 purchase totals =	$918.77		$1,002.7762	$1,002.78	$1,002.80	$1,002.90