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	$144.85	12.444%	$162.8751	$162.88	$162.90	$162.90
Purchase #2	$89.92	9.639%	$98.5874	$98.59	$98.60	$98.60
Purchase #3	$171.34	11.136%	$190.4204	$190.42	$190.40	$190.40
Purchase #4	$124.35	13.177%	$140.7356	$140.74	$140.75	$140.70
Purchase #5	$185.41	11.301%	$206.3632	$206.36	$206.35	$206.40
Purchase #6	$238.51	9.160%	$260.3575	$260.36	$260.35	$260.40
Purchase #7	$49.98	3.650%	$51.8043	$51.80	$51.80	$51.80
7 purchase totals =	$1,004.36		$1,111.1435	$1,111.15	$1,111.15	$1,111.20