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	$170.34	9.617%	$186.7216	$186.72	$186.70	$186.70
Purchase #2	$171.75	7.183%	$184.0868	$184.09	$184.10	$184.10
Purchase #3	$166.30	10.147%	$183.1745	$183.17	$183.15	$183.20
Purchase #4	$118.41	8.225%	$128.1492	$128.15	$128.15	$128.10
Purchase #5	$111.31	11.172%	$123.7456	$123.75	$123.75	$123.70
Purchase #6	$28.26	11.855%	$31.6102	$31.61	$31.60	$31.60
Purchase #7	$14.49	4.424%	$15.131	$15.13	$15.15	$15.10
7 purchase totals =	$780.86		$852.6189	$852.62	$852.60	$852.50