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	$49.33	4.437%	$51.5188	$51.52	$51.50	$51.50
Purchase #2	$33.31	5.312%	$35.0794	$35.08	$35.10	$35.10
Purchase #3	$188.39	13.497%	$213.817	$213.82	$213.80	$213.80
Purchase #4	$198.37	11.671%	$221.5218	$221.52	$221.50	$221.50
Purchase #5	$83.57	8.769%	$90.8983	$90.90	$90.90	$90.90
Purchase #6	$77.27	5.261%	$81.3352	$81.34	$81.35	$81.30
Purchase #7	$164.67	10.227%	$181.5108	$181.51	$181.50	$181.50
7 purchase totals =	$794.91		$875.6813	$875.69	$875.65	$875.60