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	$140.90	13.168%	$159.4537	$159.45	$159.45	$159.50
Purchase #2	$236.91	5.642%	$250.2765	$250.28	$250.30	$250.30
Purchase #3	$205.28	11.339%	$228.5567	$228.56	$228.55	$228.60
Purchase #4	$183.51	13.247%	$207.8196	$207.82	$207.80	$207.80
Purchase #5	$35.48	9.741%	$38.9361	$38.94	$38.95	$38.90
Purchase #6	$90.91	9.861%	$99.8746	$99.87	$99.85	$99.90
Purchase #7	$186.62	5.236%	$196.3914	$196.39	$196.40	$196.40
7 purchase totals =	$1,079.61		$1,181.3086	$1,181.31	$1,181.30	$1,181.40