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	$38.97	12.573%	$43.8697	$43.87	$43.85	$43.90
Purchase #2	$232.46	11.323%	$258.7814	$258.78	$258.80	$258.80
Purchase #3	$235.91	12.336%	$265.0119	$265.01	$265.00	$265.00
Purchase #4	$73.34	13.179%	$83.0055	$83.01	$83.00	$83.00
Purchase #5	$77.93	6.257%	$82.8061	$82.81	$82.80	$82.80
Purchase #6	$215.57	12.452%	$242.4128	$242.41	$242.40	$242.40
Purchase #7	$72.67	3.831%	$75.454	$75.45	$75.45	$75.50
7 purchase totals =	$946.85		$1,051.3414	$1,051.34	$1,051.30	$1,051.40