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	$19.90	5.377%	$20.97	$20.97	$20.95	$21.00
Purchase #2	$107.61	12.523%	$121.086	$121.09	$121.10	$121.10
Purchase #3	$243.48	6.608%	$259.5692	$259.57	$259.55	$259.60
Purchase #4	$196.92	13.679%	$223.8567	$223.86	$223.85	$223.90
Purchase #5	$99.45	11.673%	$111.0588	$111.06	$111.05	$111.10
Purchase #6	$232.86	11.294%	$259.1592	$259.16	$259.15	$259.20
Purchase #7	$41.58	11.524%	$46.3717	$46.37	$46.35	$46.40
7 purchase totals =	$941.80		$1,042.0716	$1,042.08	$1,042.00	$1,042.30