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	$25.69	12.431%	$28.8835	$28.88	$28.90	$28.90
Purchase #2	$206.90	12.762%	$233.3046	$233.30	$233.30	$233.30
Purchase #3	$196.77	12.853%	$222.0608	$222.06	$222.05	$222.10
Purchase #4	$109.97	12.473%	$123.6866	$123.69	$123.70	$123.70
Purchase #5	$174.67	6.270%	$185.6218	$185.62	$185.60	$185.60
Purchase #6	$20.25	8.364%	$21.9437	$21.94	$21.95	$21.90
Purchase #7	$131.39	3.233%	$135.6378	$135.64	$135.65	$135.60
7 purchase totals =	$865.64		$951.1388	$951.13	$951.15	$951.10