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	$89.60	7.329%	$96.1668	$96.17	$96.15	$96.20
Purchase #2	$82.34	10.372%	$90.8803	$90.88	$90.90	$90.90
Purchase #3	$44.58	6.700%	$47.5669	$47.57	$47.55	$47.60
Purchase #4	$28.65	10.554%	$31.6737	$31.67	$31.65	$31.70
Purchase #5	$40.89	10.478%	$45.1745	$45.17	$45.15	$45.20
Purchase #6	$160.57	4.870%	$168.3898	$168.39	$168.40	$168.40
Purchase #7	$154.46	3.330%	$159.6035	$159.60	$159.60	$159.60
7 purchase totals =	$601.09		$639.4555	$639.45	$639.40	$639.60