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	$82.61	6.241%	$87.7657	$87.77	$87.75	$87.80
Purchase #2	$103.45	7.355%	$111.0587	$111.06	$111.05	$111.10
Purchase #3	$84.78	11.369%	$94.4186	$94.42	$94.40	$94.40
Purchase #4	$84.31	11.265%	$93.8075	$93.81	$93.80	$93.80
Purchase #5	$64.51	12.829%	$72.786	$72.79	$72.80	$72.80
Purchase #6	$47.81	11.373%	$53.2474	$53.25	$53.25	$53.20
Purchase #7	$85.83	5.873%	$90.8708	$90.87	$90.85	$90.90
7 purchase totals =	$553.30		$603.9547	$603.97	$603.90	$604.00